{"id":546,"date":"2026-04-21T06:02:27","date_gmt":"2026-04-21T06:02:27","guid":{"rendered":"https:\/\/isbm-blow-molding.com\/?p=546"},"modified":"2026-04-21T06:04:12","modified_gmt":"2026-04-21T06:04:12","slug":"pet-bottle-whitening-haze-root-causes-and-diagnostic-guide","status":"publish","type":"post","link":"https:\/\/isbm-blow-molding.com\/fr\/pet-bottle-whitening-haze-root-causes-and-diagnostic-guide\/","title":{"rendered":"PET Bottle Whitening & Haze: Root Causes and Diagnostic Guide"},"content":{"rendered":"
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D\u00c9PANNAGE<\/p>\n

PET Bottle Whitening & Haze: Root Causes and Diagnostic Guide<\/h1>\n

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.<\/p>\n

Get an Expert Haze Diagnostic Review \u2192<\/a><\/p>\n<\/div>\n<\/section>\n

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Dans ce guide<\/h3>\n
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  1. The Three Distinct Haze Mechanisms<\/a><\/li>\n
  2. Preform Temperature: The #1 Root Cause<\/a><\/li>\n
  3. Stretch Ratio Deficiency Analysis<\/a><\/li>\n
  4. PET Moisture & Intrinsic Viscosity Issues<\/a><\/li>\n
  5. Base Pole Whitening Diagnosis<\/a><\/li>\n
  6. IR Heater Profile & Zone Optimization<\/a><\/li>\n
  7. Mould Temperature Impact<\/a><\/li>\n
  8. Step-by-Step Diagnostic Flowchart<\/a><\/li>\n
  9. \u00c9tudes de cas d'usines cor\u00e9ennes<\/a><\/li>\n
  10. Conclusion<\/a><\/li>\n<\/ol>\n<\/div>\n

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    1. The Three Distinct Haze Mechanisms<\/h2>\n

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    \"PET<\/p>\n

    Target PET bottle clarity \u2014 the baseline against which amorphous, pearlescent, and stress whitening defects are identified<\/p>\n<\/div>\n

    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.<\/p>\n

    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.<\/p>\n

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    TYPE 1<\/span><\/p>\n

    Amorphous Haze (Cloudy, Uniform Translucency)<\/h3>\n<\/div>\n

    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.<\/p>\n

    Typical trigger:<\/strong> preform too cold entering the blow station, inadequate stretch rod timing, or undersized preform design relative to bottle volume.<\/p>\n<\/div>\n

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    TYPE 2<\/span><\/p>\n

    Pearlescent Whitening (Iridescent, Shiny)<\/h3>\n<\/div>\n

    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\u00b0C crystallization window too slowly, or when preform surface temperature exceeds 115\u00b0C.<\/p>\n

    Typical trigger:<\/strong> IR heater profile too aggressive in specific zones, mould cooling inadequate in affected areas, excessive preform residence time between IR exit and blow station.<\/p>\n<\/div>\n

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    TYPE 3<\/span><\/p>\n

    Stress Whitening (Localized Streaks or Lines)<\/h3>\n<\/div>\n

    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.<\/p>\n

    Typical trigger:<\/strong> stretch rod too fast, blow air timing mismatch, asymmetric preform heating creating uneven expansion, or wall thickness distribution problems from preform geometry.<\/p>\n<\/div>\n<\/div>\n

    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.<\/p>\n

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    2. Preform Temperature: The #1 Root Cause<\/h2>\n

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    \"ISBM<\/p>\n

    ISBM preform conditioning sequence \u2014 surface temperature must stay in the 100-110\u00b0C window at blow station entry<\/p>\n<\/div>\n

    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\u00b0C surface temperature entering the blow. Below 100\u00b0C the polymer is too stiff for full stretch, producing Type 1 amorphous haze. Above 115\u00b0C the polymer begins spherulitic crystallization, producing Type 2 pearlescent whitening. The 10\u00b0C window is unforgiving \u2014 many Korean haze defects originate here.<\/p>\n

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    Temperature zone diagnostic reference:<\/strong><\/p>\n