{"id":10206,"date":"2026-11-07T01:00:00","date_gmt":"2026-11-07T01:00:00","guid":{"rendered":"https:\/\/uplastech.com\/thin-pet-rpet-lot-variation\/"},"modified":"2026-11-07T01:00:00","modified_gmt":"2026-11-07T01:00:00","slug":"thin-pet-rpet-lot-variation","status":"publish","type":"post","link":"https:\/\/uplastech.com\/pl\/thin-pet-rpet-lot-variation\/","title":{"rendered":"PET Tray Clarity Drifts as rPET Content Varies Between Lots"},"content":{"rendered":"<style>\n.upl-blog{font-size:17px;line-height:1.78;color:#1f2937}\n.upl-blog p{margin:0 0 18px}\n.upl-blog h2{font-size:26px;line-height:1.3;color:#0b2b33;margin:46px 0 14px;font-weight:700;letter-spacing:-.015em}\n.upl-blog h3{font-size:19.5px;color:#0d3b47;margin:28px 0 10px;font-weight:700}\n.upl-blog ul,.upl-blog ol{margin:0 0 20px;padding-left:22px}\n.upl-blog li{margin:0 0 9px}\n.upl-blog figure{margin:0 0 34px}\n.upl-blog figure img{width:100%;height:auto;display:block;border-radius:10px}\n.upl-blog figcaption{font-size:13px;color:#6b7280;margin-top:10px;line-height:1.5}\n.upl-blog .toc{background:none;border:0;border-radius:0;padding:0;margin:0 0 34px}\n.upl-blog .toc .lwptoc{margin:0}\n.upl-blog .toc h4{margin:0 0 10px;font-size:13px;letter-spacing:.1em;text-transform:uppercase;color:#0d5563}\n.upl-blog .toc ol{margin:0;padding-left:18px;font-size:14.5px}\n.upl-blog .toc li{margin-bottom:6px}\n.upl-blog table{width:100%;border-collapse:collapse;font-size:14.5px;margin:0 0 10px}\n.upl-blog th{background:#0d3b47;color:#fff;text-align:left;padding:11px 13px;font-weight:600;font-size:13.5px;border:0}\n.upl-blog td{padding:11px 13px;border:0;border-bottom:1px solid #e8ebed;vertical-align:top}\n.upl-blog tbody tr:nth-child(even){background:#fafbfc}\n.upl-blog .tablecap{font-size:12.5px;color:#6b7280;margin:0 0 30px}\n.upl-blog .myth{background:#fff8ef;border:1px solid #f6ddbd;border-radius:8px;padding:16px 20px;margin:0 0 26px;font-size:15.5px}\n.upl-blog .myth b{color:#a85c10}\n.upl-blog .callout{background:#f2f8f9;border-radius:8px;padding:18px 22px;margin:0 0 26px;font-size:15.5px;border-left:3px solid #14707f}\n.upl-blog .faq h3{border-top:1px solid #eceff1;padding-top:22px;margin-top:0;font-size:18px}\n.upl-blog .faq h3:first-of-type{border-top:0;padding-top:0}\n.upl-blog .cta{background:linear-gradient(135deg,#0b2b33,#0d5563);color:#fff;border-radius:12px;padding:34px;margin:48px 0 30px}\n.upl-blog .cta h2,.upl-blog .cta .cta-h{color:#fff;margin:0 0 10px;font-size:24px;font-weight:700;line-height:1.3}\n.upl-blog .cta p{color:#c9dee3;margin:0 0 20px;font-size:16px}\n.upl-blog .btn{display:inline-block;background:#e07a1f;color:#fff;text-decoration:none;font-weight:700;padding:13px 26px;border-radius:8px;font-size:15.5px}\n.upl-blog .rel{border-top:1px solid #e8ebed;margin-top:40px;padding-top:26px}\n.upl-blog .rel h4{font-size:13px;letter-spacing:.1em;text-transform:uppercase;color:#6b7280;margin:0 0 14px}\n.upl-blog .rel ul{list-style:none;padding:0;margin:0}\n.upl-blog .rel li{padding:11px 0;border-bottom:1px dashed #e8ebed}\n.upl-blog .rel a{text-decoration:none;font-weight:600;font-size:15.5px}\n\/* ==UPL-CONVERSION-MODULES-START== 2024 problem-solving \/ lead-gen blocks *\/\n.upl-blog .mod-h{font-size:12.5px;letter-spacing:.12em;text-transform:uppercase;font-weight:700;color:#0d5563;margin:0 0 12px}\n.upl-blog .problem{background:#fff8f3;border:1px solid #f3ddc9;border-left:4px solid #e07a1f;border-radius:10px;padding:22px 26px;margin:0 0 32px;font-size:16px}\n.upl-blog .problem p{margin:0 0 10px}\n.upl-blog .problem p:last-child{margin-bottom:0}\n.upl-blog .problem .mod-h{color:#a85c10}\n.upl-blog .problem .problem-promise{font-weight:700;color:#0b2b33}\n.upl-blog .steps{background:#f7fafb;border:1px solid #e1ebee;border-radius:10px;padding:22px 26px;margin:0 0 28px}\n.upl-blog .steps ol{list-style:none;counter-reset:uplst;margin:0;padding:0}\n.upl-blog .steps li{counter-increment:uplst;position:relative;padding:0 0 16px 42px;margin:0;font-size:15.5px}\n.upl-blog .steps li:last-child{padding-bottom:0}\n.upl-blog .steps li::before{content:counter(uplst);position:absolute;left:0;top:2px;width:26px;height:26px;border-radius:50%;background:#0d5563;color:#fff;font-size:13px;font-weight:700;line-height:26px;text-align:center}\n.upl-blog table.spec th{background:#14707f}\n.upl-blog .conv{background:#eef6f7;border:1px solid #cfe4e8;border-radius:10px;padding:24px 26px;margin:32px 0}\n.upl-blog .conv p{margin:0 0 12px;font-size:15.5px}\n.upl-blog .conv .conv-lbl{font-weight:700;color:#0b2b33;margin:16px 0 8px}\n.upl-blog ul.conv-need{list-style:none;padding:0;margin:0 0 20px;display:grid;grid-template-columns:1fr 1fr;gap:6px 18px}\n.upl-blog ul.conv-need li{position:relative;padding-left:20px;margin:0;font-size:14.5px}\n.upl-blog ul.conv-need li::before{content:\"\";position:absolute;left:0;top:9px;width:9px;height:9px;border:2px solid #14707f;border-radius:2px}\n.upl-blog .conv-btn{display:inline-block;background:#0d5563;color:#fff;text-decoration:none;font-weight:700;padding:11px 22px;border-radius:7px;font-size:15px}\n.upl-blog .checklist{background:#fbfcfd;border:1px solid #e3e9ec;border-radius:10px;padding:24px 26px;margin:36px 0}\n.upl-blog .checklist ul{list-style:none;padding:0;margin:0 0 12px}\n.upl-blog .checklist li{position:relative;padding-left:28px;margin:0 0 10px;font-size:15.5px}\n.upl-blog .checklist li::before{content:\"\";position:absolute;left:0;top:7px;width:14px;height:14px;border:2px solid #0d5563;border-radius:3px}\n.upl-blog .cl-note{font-size:13.5px;color:#6b7280;margin:0}\n.upl-blog .cta .cta-lbl{color:#c9dee3;font-weight:700;margin:0 0 8px;font-size:14.5px}\n.upl-blog ul.cta-need{list-style:none;padding:0;margin:0 0 22px;display:grid;grid-template-columns:1fr 1fr;gap:4px 18px}\n.upl-blog ul.cta-need li{color:#e4f0f2;font-size:14.5px;padding-left:18px;position:relative;margin:0}\n.upl-blog ul.cta-need li::before{content:\"\\2713\";position:absolute;left:0;color:#e07a1f;font-weight:700}\n\/* ==UPL-CONVERSION-MODULES-END== *\/\n@media(max-width:640px){.upl-blog h2{font-size:22px}.upl-blog table{font-size:13px}.upl-blog .cta{padding:24px}.upl-blog ul.conv-need,.upl-blog ul.cta-need{grid-template-columns:1fr}.upl-blog .problem,.upl-blog .steps,.upl-blog .conv,.upl-blog .checklist{padding:18px}}\n\/* Single-post: hide the greeting card, keep the round WhatsApp bubble.\n   The Click to Chat logic refuses to open a chat while the greeting node exists,\n   so Code Snippets #9 removes that node from the DOM. This rule is only the visual fallback.\n   Delete #9 before removing this rule. *\/\nbody.single-post .ht_ctc_chat_greetings_box{display:none !important}\n<\/style>\n<div class=\"upl-blog\">\n<figure><img decoding=\"async\" src=\"https:\/\/uplastech.com\/wp-content\/uploads\/2026\/10\/thermoforming-medical-packaging.jpg\" alt=\"PET Tray Clarity Drifts as rPET Content Varies Between Lots\" \/><figcaption>Thin-wall forming: a production part is the only useful reference for a discussion about process drift.<\/figcaption><\/figure>\n<p class=\"lead\">PET trays come off the line with a different tint or haze from one sheet lot to the next when recycled content is not held within a declared band.<\/p>\n<div class=\"toc\"><\/div>\n<h2 id=\"what\">What the failure looks like on the line<\/h2>\n<p>PET thin-wall packs are bought for clarity and shelf presentation, so a functional tray can still be rejected on the way it looks under cabinet lighting.<\/p>\n<p>Two production lots of the same PET tray differ in haze or slight yellow cast under the same light, and the formed wall thickness drifts with the change.<\/p>\n<p>Recycled PET carries variable intrinsic viscosity, colour and contaminant level, which shift crystallisation and melt strength during forming. As the regrind ratio moves between lots, the sheet draws and cools differently, so clarity and gauge move with it.<\/p>\n<p>The useful question is not whether the part conforms, but which condition was never written into the specification. On a buyer's specification this distinction matters: a part can measure inside tolerance and still fail in use, because the drawing records geometry while the complaint records behaviour. rPET content is usually the first value both sides compare, and it is also the one most often quoted without the conditions attached to it.<\/p>\n<h2 id=\"window\">The process window that decides it<\/h2>\n<p>Four variables move this result more than the rest. The ranges below are illustrative engineering guidance for a first discussion; confirm them on your own tool, material grade and part geometry before they become contract terms.<\/p>\n<table>\n<thead>\n<tr>\n<th>Zmienna<\/th>\n<th>Typical window<\/th>\n<th>What fails outside it<\/th>\n<\/tr>\n<\/thead>\n<tbody>\n<tr>\n<td>rPET content<\/td>\n<td>20-50 %<\/td>\n<td>Higher or shifting ratios change haze and draw behaviour<\/td>\n<\/tr>\n<tr>\n<td>Intrinsic viscosity<\/td>\n<td>0.72-0.84 dL\/g<\/td>\n<td>Low IV thins the wall and raises brittleness<\/td>\n<\/tr>\n<tr>\n<td>Sheet drying dew point<\/td>\n<td>-30 to -40 C<\/td>\n<td>Wet regrind hydrolyses and adds haze<\/td>\n<\/tr>\n<tr>\n<td>Lot-to-lot haze delta<\/td>\n<td>0-3 %<\/td>\n<td>Larger deltas are visible on the shelf<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<p class=\"tablecap\">Table 1. Starting window for a joint process trial. Values are engineering guidance, not a measured survey.<\/p>\n<p><b>rPET content<\/b> is typically held at 20-50 %. Higher or shifting ratios change haze and draw behaviour Record it together with the measurement point and the moment in the cycle; a single number without a location is not a process setting.<\/p>\n<p><b>Intrinsic viscosity<\/b> is typically held at 0.72-0.84 dL\/g. Low IV thins the wall and raises brittleness When this drifts, the symptom usually appears at one cavity, one sheet position or one lane before it appears across the whole batch.<\/p>\n<p><b>Sheet drying dew point<\/b> is typically held at -30 to -40 C. Wet regrind hydrolyses and adds haze A change here is cheap during a trial and expensive after tooling release, so treat it as a controlled variable with a documented re-approval.<\/p>\n<p><b>Lot-to-lot haze delta<\/b> is typically held at 0-3 %. Larger deltas are visible on the shelf Put it on the change-control list, otherwise an unannounced material or setting substitution will be mistaken for ordinary process noise.<\/p>\n<h2 id=\"response\">Reading the response curve<\/h2>\n<figure><img decoding=\"async\" src=\"https:\/\/uplastech.com\/wp-content\/uploads\/2026\/11\/thin-pet-rpet-lot-variation-chart.jpg\" alt=\"PET Tray Clarity Drifts as rPET Content Varies Between Lots: Clarity retention (%) against rPET content (%)\" \/><figcaption>Figure 1. Left: Clarity retention (%) against rPET content (%). Right: how audited failures of this type typically split by cause. All plotted values are illustrative engineering guidance, not a measured survey.<\/figcaption><\/figure>\n<p>The left panel shows clarity retention (%) as rpet content (%) increases: the response falls from 94 to 18 on the illustrative 0&ndash;100 scale. The dashed line at 60 marks a proposed acceptance limit, not a universal standard. Move that line only after the test method and the sample plan have been agreed, otherwise two suppliers can both be compliant and still deliver different parts.<\/p>\n<p>Read the shape rather than a single point. A curve that changes quickly near the limit is more sensitive to ordinary process noise than one that approaches it gradually, and that difference should be reflected in how tightly the setting is controlled and how often it is checked.<\/p>\n<h2 id=\"causes\">Where the causes actually sit<\/h2>\n<p>The right panel of Figure 1 splits audited failures of this type into five groups. The percentages are illustrative engineering guidance for prioritising an investigation, not a measured survey and not a prediction for your line.<\/p>\n<table>\n<thead>\n<tr>\n<th>Przyczyna<\/th>\n<th>Illustrative share<\/th>\n<th>First check<\/th>\n<\/tr>\n<\/thead>\n<tbody>\n<tr>\n<td>Shifting rPET ratio<\/td>\n<td>35%<\/td>\n<td>Record the declared recycled content for each incoming sheet lot.<\/td>\n<\/tr>\n<tr>\n<td>Variable flake colour<\/td>\n<td>25%<\/td>\n<td>Measure haze on a formed tray from each lot under a fixed light source.<\/td>\n<\/tr>\n<tr>\n<td>Low intrinsic viscosity<\/td>\n<td>18%<\/td>\n<td>Compare formed wall gauge between the current and previous lot.<\/td>\n<\/tr>\n<tr>\n<td>Wet regrind<\/td>\n<td>13%<\/td>\n<td>Check the sheet drying log for the lot before forming.<\/td>\n<\/tr>\n<tr>\n<td>Different cooling history<\/td>\n<td>9%<\/td>\n<td>Keep a retained tray from each approved lot for side-by-side review.<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<p class=\"tablecap\">Table 2. Cause split and the corresponding first check. Shares are indicative and sum to 100.<\/p>\n<p><b>Shifting rPET ratio<\/b> accounts for roughly 35% of the illustrative split. Record the declared recycled content for each incoming sheet lot. Start here before authorising a material or tooling change, because it is the fastest explanation to confirm or eliminate.<\/p>\n<p><b>Variable flake colour<\/b> accounts for roughly 25% of the illustrative split. Measure haze on a formed tray from each lot under a fixed light source. Start here before authorising a material or tooling change, because it is the fastest explanation to confirm or eliminate.<\/p>\n<p><b>Low intrinsic viscosity<\/b> accounts for roughly 18% of the illustrative split. Compare formed wall gauge between the current and previous lot. Start here before authorising a material or tooling change, because it is the fastest explanation to confirm or eliminate.<\/p>\n<h2 id=\"checks\">Checks before sign-off<\/h2>\n<p>Work through these in order; measuring a later variable before an earlier one hides the cause rather than finding it.<\/p>\n<ol>\n<li>Record the declared recycled content for each incoming sheet lot.<\/li>\n<li>Measure haze on a formed tray from each lot under a fixed light source.<\/li>\n<li>Compare formed wall gauge between the current and previous lot.<\/li>\n<li>Check the sheet drying log for the lot before forming.<\/li>\n<li>Keep a retained tray from each approved lot for side-by-side review.<\/li>\n<\/ol>\n<p>Keep a retained reference sample beside every result. When a batch is disputed, the comparison that settles it is almost always between the retained part and the current one under the same method, not between either part and a number on a drawing. Record the instrument, the operator, the conditioning time and the position on the part or sheet for each reading.<\/p>\n<h2 id=\"specification\">Writing it into the specification and the evidence pack<\/h2>\n<p>Haze and colour shift between consecutive approved lots shall stay within the agreed band measured on formed trays under a defined light source.<\/p>\n<p>Write the requirement as a behaviour at a stated condition, not as a brand of material or a machine setting. State the test method, the conditioning, the sample plan and the rule for deciding a pass. Where a document is needed, ask the supplier for documentation that covers the actual construction and check its scope against your own market before approval; a document for the base material alone does not describe the finished part you are buying.<\/p>\n<p>At first-article approval, freeze the drawing revision, the material and colour identification, the process window, the tool and cavity identification, and the inspection method. Any later change to grade, site, tool, or window should trigger a new first article rather than a paper waiver. Keep retained samples from the approved lot and from each production lot so that a future comparison is possible.<\/p>\n<table>\n<thead>\n<tr>\n<th>Evidence item<\/th>\n<th>What it must show<\/th>\n<\/tr>\n<\/thead>\n<tbody>\n<tr>\n<td>Approved drawing and revision<\/td>\n<td>The exact geometry and tolerances the decision applies to<\/td>\n<\/tr>\n<tr>\n<td>Material and colour identification<\/td>\n<td>Grade, supplier, colour reference and any declared recycled content<\/td>\n<\/tr>\n<tr>\n<td>Process window and change log<\/td>\n<td>The agreed settings and any deviation since approval<\/td>\n<\/tr>\n<tr>\n<td>Inspection record and retained samples<\/td>\n<td>Method, conditions, results and a physical reference from the same lot<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<p class=\"tablecap\">Table 3. Minimum evidence pack for a first-article decision and a later batch dispute.<\/p>\n<p>The values quoted here are illustrative engineering guidance, not a measured survey. Agree the test method, the sample size and the acceptance rule before comparing numbers across suppliers.<\/p>\n<div class=\"faq\">\n<h2 id=\"questions\">Questions buyers ask<\/h2>\n<h3>Is this a material problem or a process problem?<\/h3>\n<p>Recycled PET carries variable intrinsic viscosity, colour and contaminant level, which shift crystallisation and melt strength during forming. As the regrind ratio moves between lots, the sheet draws and cools differently, so clarity and gauge move with it. It is worth separating the two before a supplier changes a grade: hold the material constant for one controlled run, then move one setting at a time. If the symptom follows the setting, the material was never the cause.<\/p>\n<h3>Can rpet content be traded against cycle time?<\/h3>\n<p>Only within the window stated in Table 1, and only with a recorded trial. Higher or shifting ratios change haze and draw behaviour A faster cycle that sits outside the window usually moves the failure downstream, where it costs more to find.<\/p>\n<h3>What should be recorded at incoming inspection?<\/h3>\n<p>Keep the measurement, the method, the sample identity and the conditions together. Record the declared recycled content for each incoming sheet lot. A result without its conditions cannot be compared with a later batch.<\/p>\n<h3>Does a change of PET require re-approval?<\/h3>\n<p>Treat any change to material grade, tool, site or process window as a change that needs a new first-article decision. For thin-wall forming work the drawing alone is not enough; the process route is part of what was approved.<\/p>\n<h3>How many samples are enough for a first-article decision?<\/h3>\n<p>There is no universal number. Sample across cavities, lanes, sheet positions or reel lengths so that the spread is visible, not just the average. Agree the sample plan and the acceptance rule with the supplier before the trial starts.<\/p>\n<h3>What belongs in the evidence pack?<\/h3>\n<p>The approved drawing and revision, the material and colour identification, the process window, the inspection method and results, the retained reference samples, and documentation covering the actual construction. Ask the supplier to state the scope of each document and check it against your own market.<\/p>\n<\/div>\n<div class=\"cta\">\n<p class=\"cta-h\">Seeing this on a current thin-wall forming job?<\/p>\n<p>Send the drawing, the material and grade, the process window you are running, and the point in the cycle or the shelf life where the fault appears. We will help you separate a material question from a process question and a specification question before anyone changes a tool.<\/p>\n<p><a class=\"btn\" href=\"https:\/\/uplastech.com\/pl\/kontakt\/\">Talk to our thin-wall forming team<\/a><\/p>\n<\/div>\n<div class=\"rel\">\n<h4>Continue reading<\/h4>\n<ul>\n<li><a href=\"https:\/\/uplastech.com\/pl\/pet-rpet-thermoforming\/\">PET and rPET Thermoforming: Crystallinity, Drying and the Forming Window<\/a><\/li>\n<li><a href=\"https:\/\/uplastech.com\/pl\/pet-sheet-regrind-clarity-haze-limit\/\">PET Sheet Regrind and Haze: Setting a Clarity Ceiling on the Sheet Order<\/a><\/li>\n<li><a href=\"https:\/\/uplastech.com\/pl\/sheet-lot-change-approval-notification\/\">Sheet Lot Changes: The Change-Notification Clause That Protects the Forming Window<\/a><\/li>\n<li><a href=\"https:\/\/uplastech.com\/pl\/pet-sheet-extrusion\/\">PET Sheet: Water Is Measured in Parts per Million and It Decides Everything<\/a><\/li>\n<li><a href=\"https:\/\/uplastech.com\/pl\/recycled-content-declaration-thermoformed-trays\/\">Recycled Content: State the Calculation Basis<\/a><\/li>\n<\/ul>\n<\/div>\n<\/div>","protected":false},"excerpt":{"rendered":"<p>PET trays come off the line with a different tint or haze from one sheet lot to the next when recycled content is not held within a declared band.<\/p>","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[29],"tags":[],"class_list":["post-10206","post","type-post","status-publish","format-standard","hentry","category-vacuum-forming"],"meta_box":{"post-to-quiz_to":[]},"_links":{"self":[{"href":"https:\/\/uplastech.com\/pl\/wp-json\/wp\/v2\/posts\/10206","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/uplastech.com\/pl\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/uplastech.com\/pl\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/uplastech.com\/pl\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/uplastech.com\/pl\/wp-json\/wp\/v2\/comments?post=10206"}],"version-history":[{"count":0,"href":"https:\/\/uplastech.com\/pl\/wp-json\/wp\/v2\/posts\/10206\/revisions"}],"wp:attachment":[{"href":"https:\/\/uplastech.com\/pl\/wp-json\/wp\/v2\/media?parent=10206"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/uplastech.com\/pl\/wp-json\/wp\/v2\/categories?post=10206"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/uplastech.com\/pl\/wp-json\/wp\/v2\/tags?post=10206"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}