문제 해결
PET Bottle Whitening & Haze: Root Causes and Diagnostic Guide
Haze and whitening defects can scrap 10-20% of daily PET bottle output overnight. The root cause is almost never obvious from visual inspection alone. This guide walks through the three distinct whitening mechanisms, their specific diagnostic signatures, and the measurable process parameters Korean production engineers should adjust first for each failure mode.
이 가이드에서
1. The Three Distinct Haze Mechanisms
Target PET bottle clarity — the baseline against which amorphous, pearlescent, and stress whitening defects are identified
Most production engineers use “haze” as a single term. In reality, PET bottle whitening arises from three mechanistically distinct failures, each with different root causes and different process corrections. Misidentifying the mechanism means correcting the wrong process variable, leaving the actual defect unresolved and creating new defects in the corrected area. A Korean beverage bottler in Ansan running 4 million bottles monthly cannot afford trial-and-error diagnostics. The first diagnostic step is always identifying which of the three mechanisms is producing the haze.
The three mechanisms are amorphous haze (light scattering from insufficiently stretched PET chains), pearlescent whitening (micro-crystallization from over-heating), and stress whitening (mechanical stress cracking along molecular alignment lines). Each produces visually different defect patterns, concentrates in different bottle zones, and demands different process adjustments. The diagnostic cards below explain how to identify each on your production line.
TYPE 1
Amorphous Haze (Cloudy, Uniform Translucency)
Appearance: milky, cloudy translucency uniformly distributed across the bottle body. Light passes through but scatters, giving the bottle a frosted appearance rather than crystalline clarity. The defect typically affects the entire bottle body, not localized zones. Root cause: insufficient biaxial stretching during blow, leaving random-oriented PET chains that scatter light like fog droplets.
Typical trigger: preform too cold entering the blow station, inadequate stretch rod timing, or undersized preform design relative to bottle volume.
TYPE 2
Pearlescent Whitening (Iridescent, Shiny)
Appearance: shimmering pearl-like whiteness with subtle iridescent shift when rotated in light. Typically concentrates at the base pole, neck-to-shoulder transition, or gate vestige zones. Root cause: spherulitic crystallization of PET when the polymer cools through the 120-180°C crystallization window too slowly, or when preform surface temperature exceeds 115°C.
Typical trigger: IR heater profile too aggressive in specific zones, mould cooling inadequate in affected areas, excessive preform residence time between IR exit and blow station.
TYPE 3
Stress Whitening (Localized Streaks or Lines)
Appearance: sharp whitish streaks or lines along molecular-alignment directions, most commonly vertical striations on bottle body or radial lines at shoulder. Defect intensifies under flexion or squeeze testing. Root cause: localized mechanical stress exceeds the elastic deformation limit of already-aligned polymer chains, creating micro-voids that scatter light.
Typical trigger: stretch rod too fast, blow air timing mismatch, asymmetric preform heating creating uneven expansion, or wall thickness distribution problems from preform geometry.
Correct mechanism identification unlocks correct process adjustment. The remainder of this guide walks through each root cause category, the specific process parameters that drive it, and the adjustment ranges Korean production engineers should try first.
2. Preform Temperature: The #1 Root Cause
ISBM preform conditioning sequence — surface temperature must stay in the 100-110°C window at blow station entry
Preform surface temperature at the blow station is the single most impactful variable controlling bottle clarity. PET has an optimal processing window of 100-110°C surface temperature entering the blow. Below 100°C the polymer is too stiff for full stretch, producing Type 1 amorphous haze. Above 115°C the polymer begins spherulitic crystallization, producing Type 2 pearlescent whitening. The 10°C window is unforgiving — many Korean haze defects originate here.
Temperature zone diagnostic reference:
- ▸Below 95°C: severe under-stretching, Type 1 amorphous haze, risk of burst rejection
- ▸95-99°C: marginal zone, partial amorphous haze, inconsistent wall distribution
- ▸100-110°C: optimal processing window, clear bottles, full biaxial orientation
- ▸111-114°C: marginal zone, slight surface softness, risk of localized pearlescence
- ▸Above 115°C: crystallization onset, Type 2 pearlescent whitening guaranteed
For one-step ISBM machines including our HGY150-V4 and HGY250-V4 platforms, the preform exits the injection station and cools to blow temperature during the indexing rotation. The conditioning time is built into machine architecture. Preform surface temperature measurement should use a calibrated IR pyrometer aimed at the bottle body center of the preform at blow station entry. Korean operators in Ansan and Incheon factories typically log this reading every shift and alert on deviations beyond ±2°C.
!
Seasonal Temperature Drift Warning
Korean factory ambient temperatures swing 25°C between summer (July average 32°C in Daegu) and winter (January average -3°C in Seoul metro). Preform conditioning profiles calibrated in spring will drift 3-5°C off target by midsummer. Rebalance IR heater zone profiles at every quarterly calibration to maintain clarity.
3. Stretch Ratio Deficiency Analysis
Full PET clarity requires total biaxial stretch of approximately 12 to 14 (axial ratio multiplied by hoop ratio). Korean beverage bottle production typically targets 2.5-3.0× axial and 4.0-4.5× hoop, yielding 10-13.5 total stretch. Insufficient total stretch leaves random-oriented polymer zones that scatter light, producing Type 1 amorphous haze even with correct preform temperature. The failure mode is most common on new bottle designs where preform geometry was not correctly sized for the finished bottle volume.
AXIAL
Axial Ratio Below 2.5×
Axial stretch below 2.5× produces haze concentrated in the vertical mid-section of the bottle body. Common root causes: preform length too long relative to finished bottle height (reducing mechanical stretch requirement), stretch rod not reaching full extension, or preform-to-bottle height ratio geometry mismatch. Fix by shortening preform length or redesigning base pole geometry to allow greater effective stretch.
HOOP
Hoop Ratio Below 4.0×
Hoop stretch below 4.0× produces haze concentrated around the circumferential direction of the bottle body, especially visible in the belly zone. Root cause: preform outer diameter too large relative to bottle maximum diameter. Fix by reducing preform OD (typically 22-28mm for 500ml beverage bottles) or increasing bottle body diameter if brand design allows.
ASYMMETRIC
Uneven Wall Thickness Distribution
Uneven circumferential wall thickness produces spot haze on thicker side, spot thinning or bursting on thinner side. Root cause: asymmetric preform heating (one IR zone running hotter than opposite side), bent preform entering blow station, or preform injection gate vestige too large creating flow asymmetry. Fix by rebalancing IR zone power distribution and verifying preform geometry meets specification.
For detailed preform design sizing calculations, see our 프리폼 디자인 가이드. Preform geometry changes require new mould investment, so Korean factory teams should verify the stretch ratio hypothesis with measurement before committing to tooling modification.
4. PET Moisture & Intrinsic Viscosity Issues
PET resin must be dried to below 50 ppm residual moisture (0.005%) before injection. Inadequate drying causes hydrolysis during melt processing, breaking polymer chains and reducing intrinsic viscosity (IV). Lower IV produces weaker melt strength, poor preform clarity, and acetaldehyde generation that degrades bottle clarity. Many Korean factories running continuous production underestimate the dryer maintenance cycle, allowing moisture drift that gradually degrades bottle clarity over several weeks.
PET moisture & IV diagnostic checklist:
- ✓Measure incoming PET resin IV (should be 0.80-0.84 dl/g for bottle grade)
- ✓Verify dryer dew point below -40°C for 4-6 hours before production
- ✓Confirm dryer outlet resin moisture below 50 ppm (Karl Fischer titration)
- ✓Check dryer desiccant bed age (replace every 24 months for Korean humid-summer climate)
- ✓Measure post-injection preform IV (should be ≥ 0.76 dl/g, IV loss < 0.05)
- ✓Verify dryer hopper insulation is intact (heat loss accelerates moisture rebound)
An IV loss greater than 0.08 dl/g from resin to finished bottle is a reliable indicator of excess moisture hydrolysis or over-temperature barrel degradation. Korean humid climate during the June-September monsoon season accelerates moisture pickup if dryer dew point drifts even marginally. K-beauty bottle producers in Suwon and pharmaceutical bottle specialists in Daejeon tighten dryer maintenance schedules specifically during this seasonal window.
5. Base Pole Whitening Diagnosis
ISBM mould base insert with cooling channels — inadequate base cooling causes pearlescent whitening at the gate vestige
A specific haze pattern deserves dedicated diagnostic attention: whitening concentrated at the bottom pole (gate area) of the bottle while the body remains clear. This is almost always a Type 2 pearlescent whitening driven by inadequate cooling of the base gate vestige. The base pole contains residual gate material from injection that cools slower than the thin bottle body wall, allowing crystallization during the cooling cycle.
SOLUTION 1
Base Mould Cooling Channel Verification
Base mould cooling channels route chilled water (typically 8-12°C) through the base insert. Scale buildup in cooling channels reduces heat transfer and allows crystallization temperature to persist. Flush base cooling channels with descaling solution every 6 months, and verify base insert surface temperature stays below 25°C during production. Pair with properly sized industrial chiller infrastructure for sustained cooling capacity.
SOLUTION 2
Gate Vestige Thickness Reduction
Preform gate diameter directly controls finished bottle gate vestige mass. A 1.5mm gate leaves roughly 3-4mm gate vestige; a 1.2mm gate leaves 2-3mm vestige with noticeably better base clarity. Reducing gate diameter requires hot runner tip adjustment and new custom mould modification, but eliminates the root cause rather than treating the symptom.
SOLUTION 3
Stretch Rod Base Geometry Optimization
Stretch rod tip geometry determines how the preform base area gets pushed into the mould base during stretch. A sharp or aggressive rod tip creates uneven base material distribution with thick zones that crystallize. Rounded rod tips distribute material more evenly, maintaining consistent wall thickness through the base transition zone. Verify stretch rod tip profile matches the bottle base geometry specification.
6. IR Heater Profile & Zone Optimization
Modern ISBM machines use multi-zone IR heater arrays to control preform temperature profile along its length. Each zone independently sets power output to compensate for preform geometry differences — thicker bottom requires more energy, thinner body requires less. Incorrect zone profiles create localized hot or cold spots that produce localized haze. Zone imbalance is one of the most common root causes of recurring haze defects on mature production lines.
IR heater diagnostic sequence:
- ▸Verify each IR tube is functional — dead tubes reduce zone power by 10-15% per tube
- ▸Clean IR reflector surfaces monthly — dust accumulation reduces efficiency 8-12% per 1000 hours
- ▸Measure preform surface temperature at each zone exit with calibrated pyrometer
- ▸Check preform rotation uniformity during IR passage (uneven rotation creates asymmetric heating)
- ▸Balance zone powers so temperature profile matches preform wall thickness profile
- ▸Monitor ambient conditions — plant HVAC changes shift effective IR absorption
IR tube replacement timing is a common oversight. Quartz IR tubes slowly lose output over roughly 8,000 hours of operation. A Korean factory running 24/7 burns through useful IR tube life in approximately 10-12 months. Scheduling preventive IR tube replacement on a calendar basis rather than failure basis prevents creeping preform under-heating that gradually increases haze rejection rates.
7. Mould Temperature Impact
Blow mould temperature controls how fast the freshly stretched bottle cools against the mould wall. Target mould surface temperature is 8-18°C, maintained by chilled water circulation through integrated cooling channels. Too cold (below 5°C) produces thermal shock that creates Type 3 stress whitening. Too warm (above 25°C) allows crystallization zones to persist, producing Type 2 pearlescent whitening. The 10°C operating window is well within modern chiller capability but requires proper sizing for sustained high-cycle production.
Chiller capacity sizing is often the root cause of gradual mould temperature drift. As production volume scales up (more cavities, faster cycles), heat input to the mould increases but the existing chiller remains the same capacity. During peak summer months in Busan and Incheon when ambient cooling water temperature rises, the chiller operates at marginal capacity and mould surface temperature creeps upward. Many Korean factories running 4-6 cavity configurations need chiller capacity upgraded to 15-25% above the nominal heat removal requirement to account for seasonal variation and future scale.
!
Korean Summer Chiller Load Warning
July-August ambient conditions in Ansan/Incheon factories can push cooling water supply temperature from 12°C spring baseline to 18-20°C midsummer. Chiller delta-T drops proportionally, mould surface temperature drifts upward 3-5°C, and haze defect rates rise 2-4% seasonally. Pre-position chiller maintenance and capacity verification before Korean summer production peaks.
8. Step-by-Step Diagnostic Flowchart
When haze defects appear on a previously healthy production line, Korean production engineers should work through this sequence in order. Each step either isolates the root cause or eliminates it from the candidate list before moving to the next.
1
Identify Haze Type (Visual Classification)
Inspect representative defective bottles under daylight and directional lighting. Classify as Type 1 amorphous (uniform cloudy), Type 2 pearlescent (iridescent shine), or Type 3 stress (localized streaks). The type identification directs the next diagnostic step.
2
Measure Preform Temperature at Blow Station
Use calibrated IR pyrometer to measure surface temperature at preform body center. Target 100-110°C. Out-of-range readings immediately isolate IR heater profile or zone balance as the root cause. In-range readings proceed to step 3.
3
Verify Mould Surface Temperature
Contact thermometer or IR surface pyrometer on mould body during operation. Target 8-18°C. Out-of-range isolates chiller capacity or cooling channel issues. Check base insert separately — base should be <25°C for Type 2 pearlescent at pole.
4
Test PET Resin Moisture & IV
Karl Fischer moisture test on resin at dryer outlet (target <50 ppm). Lab IV on both incoming resin and finished bottle (target IV loss < 0.05 dl/g). Out-of-spec indicates dryer maintenance or moisture handling issue.
5
Verify Stretch Ratio Calculation
Measure preform dimensions and finished bottle dimensions. Calculate axial ratio (bottle length / preform length) and hoop ratio (bottle max OD / preform OD). Target total ratio ≥ 10. Low values indicate preform geometry mismatch requiring tooling modification.
6
Escalate to Manufacturer Engineering Support
If steps 1-5 do not isolate the root cause, contact the machine manufacturer engineering team. Korean Ever-Power customers get 24-48 hour on-site diagnostic support from regional engineering hubs covering Seoul metro, Busan, and Daegu regions.
9. 한국 공장 사례 연구
Korean ISBM production facilities — diagnostic lessons from Gimhae, Suwon, and Daejeon installations
Three recent diagnostic cases from Korean Ever-Power installations illustrate how these principles apply in production practice.
Case Study 1 · Gimhae Beverage Bottler
Seasonal Base Pole Whitening (2 Million 500ml Bottles/Month)
징후: Type 2 pearlescent whitening at base pole appeared in July, affecting roughly 8% of production. Bottle body remained clear.
진단: Chiller cooling water temperature had drifted from 11°C spring baseline to 17°C midsummer. Base insert surface temperature rose from 18°C to 28°C, crossing crystallization threshold at the gate vestige.
해결: Chiller capacity upgraded 25%, cooling water redirected through supplementary heat exchanger. Base whitening defect rate returned to below 0.5% within 72 hours.
Case Study 2 · Suwon K-Beauty Contract Filler
Uniform Body Haze on 150ml Serum Bottles
징후: Type 1 amorphous haze appeared on new 150ml serum bottle SKU. Previous 120ml SKU with same preform produced clear bottles.
진단: Preform OD 24mm was oversized for new 38mm bottle body. Hoop ratio dropped to 3.8×, below the 4.0× minimum threshold for full biaxial orientation.
해결: New preform with 21mm OD commissioned via custom tooling delivering 4.5× hoop ratio. Bottle clarity restored to premium K-beauty standard.
Case Study 3 · Daejeon Pharmaceutical Bottler
Type 3 Stress Whitening on 15ml Eye-Drop Bottles
징후: Vertical stress whitening streaks appeared on bottle body after three weeks of stable production. Rejection rate climbed from 1% to 6% over 10 days.
진단: 스트레치 로드 서보 드라이브에서 간헐적인 속도 제어 변동이 발생했는데, 이는 로드가 프리폼 폴리머의 흐름 속도보다 빠르게 가속되어 응력 집중대가 생성되는 현상입니다.
해결: 서보 드라이브 엔코더를 교체하고 PID 튜닝을 재보정했습니다. 오실로스코프로 스트레치 속도 프로파일을 확인했습니다. 재가동 후 불량률이 0.8% 미만으로 돌아왔습니다.
10. 결론
PET 병의 백화 및 혼탁 현상은 정확한 원인을 파악하면 해결 가능한 결함입니다. 한국 생산 라인에서 발생하는 혼탁 문제의 대부분은 다음 다섯 가지 근본 원인 중 하나에서 비롯됩니다. 부적절한 프리폼 온도, 불충분한 연신율, PET의 수분 또는 IV 열화, 베이스 폴 냉각 부족, 또는 IR 히터 영역 불균형. 체계적인 진단 절차를 통해 시행착오를 거쳐 며칠씩 조정하는 대신 2~3시간 내에 원인을 찾아낼 수 있습니다.
안산, 부산, 대전, 인천에 위치한 한국 생산 엔지니어들은 반복되는 헤이즈 결함 문제를 해결하기 위해 먼저 헤이즈 유형을 정확하게 분류하고, 주요 공정 변수를 목표 범위와 비교하여 측정하고, 결함이 발생할 가능성이 있는 부분을 순차적으로 제거해야 합니다. 대부분의 결함은 이러한 초기 세 단계 진단 과정에서 해결됩니다. 측정 가능한 모든 변수가 규격 범위 내에 있지만 결함이 지속되는 경우에만 제조업체 엔지니어링 지원팀에 문의해야 합니다.
안개 진단 주요 요점
- ✓먼저 안개 유형을 비정형(균일), 진주광택(반짝임) 또는 응력(국부적인 줄무늬)으로 분류합니다.
- ✓블로우 성형 공정 진입 시 프리폼 온도는 100~110°C 범위 내에 유지되어야 합니다.
- ✓완전한 이축 배향을 위해서는 총 신장률이 10 이상이어야 합니다.
- ✓PET 수지의 수분 함량이 50ppm 미만이면 가수분해로 인한 점도 손실을 방지할 수 있습니다.
- ✓금형 표면 온도는 8~18°C, 베이스 인서트 온도는 25°C 미만으로 유지해야 진주광택 백화 현상을 방지할 수 있습니다.
- ✓한국의 여름철 냉방 부하에는 봄철 기준치 대비 15~25%의 용량 여유가 필요합니다.
- ✓석영 적외선 튜브는 8,000 작동 시간마다 예방적 교체가 필요합니다.
- ✓체계적인 진단 절차를 통해 시행착오를 거치는 데 며칠이 걸리는 대신 2~3시간 내에 근본 원인을 파악할 수 있습니다.
미세먼지 진단 전문가의 도움이 필요하신가요?
불량 패턴 사진, 현재 프리폼 온도 및 스트레치 비율 데이터, 그리고 기계 모델을 보내주시면, 저희 한국 엔지니어링 팀에서 24시간 이내에 구체적인 조정 권장 사항이 포함된 진단 보고서를 제공해 드립니다. 매개변수 조정으로 불량이 해결되지 않을 경우 현장 기술자 파견 서비스도 제공합니다.
