{"id":7825,"date":"2025-10-21T09:00:00","date_gmt":"2025-10-21T08:00:00","guid":{"rendered":"https:\/\/uplastech.com\/cpet-ovenable-trays\/"},"modified":"2025-10-21T09:00:00","modified_gmt":"2025-10-21T08:00:00","slug":"cpet-ovenable-trays","status":"publish","type":"post","link":"https:\/\/uplastech.com\/pt\/cpet-ovenable-trays\/","title":{"rendered":"CPET Ovenable Trays: Dual-Ovenable From a Thermoformer"},"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@media(max-width:640px){.upl-blog h2{font-size:22px}.upl-blog table{font-size:13px}.upl-blog .cta{padding:24px}}\n\/* \u5355\u7bc7\u9875\u9690\u85cf WhatsApp \u95ee\u5019\u5361\uff0c\u53ea\u4fdd\u7559\u5706\u5f62\u6c14\u6ce1\uff0c\u907f\u514d\u906e\u6321\u4fa7\u680f\u8be2\u76d8\u63d0\u4ea4\u6309\u94ae\u3002\n   \u6ce8\u610f\uff1aClick to Chat \u7684\u70b9\u51fb\u903b\u8f91\u662f\u300c\u95ee\u5019\u5361\u5143\u7d20\u5b58\u5728\u5c31\u4e0d\u8df3\u8f6c\u300d\uff0c\u53ea\u9760 CSS \u9690\u85cf\u4f1a\u8ba9\u6c14\u6ce1\u53d8\u6210\u6b7b\u94fe\u63a5\u3002\n   Code Snippets #9\u300cUPL single post: WhatsApp bubble jumps straight to chat\u300d\u8d1f\u8d23\u628a\u8be5\u8282\u70b9\u4ece DOM \u79fb\u9664\uff0c\n   \u4e0b\u9762\u8fd9\u6761 CSS \u53ea\u662f\u79fb\u9664\u524d\u7684\u89c6\u89c9\u515c\u5e95\u3002\u5220 #9 \u524d\u5fc5\u987b\u5148\u5220\u8fd9\u6761\u89c4\u5219\u3002 *\/\nbody.single-post .ht_ctc_chat_greetings_box{display:none !important}\n<\/style>\n<div class=\"upl-blog\">\n<figure>\n<img fetchpriority=\"high\" decoding=\"async\" src=\"https:\/\/uplastech.com\/wp-content\/uploads\/2026\/10\/cpet-ovenable-trays.jpg\" alt=\"Crystallinity against mould temperature and cycle time against mould temperature for CPET trays\" width=\"1536\" height=\"909\"><figcaption>Crystallinity climbs steeply between 120 and 160 degrees, and cycle time climbs with it.<\/figcaption><\/figure>\n<div class=\"toc\"><\/div>\n<h2 id=\"what-cpet-is\">What CPET is, and what it is not<\/h2>\n<p>CPET is crystallised polyethylene terephthalate. The polymer is the same one in a water bottle. What differs is the thermal history: a bottle is quenched amorphous, a CPET tray is held hot long enough for the chains to organise into crystallites.<\/p>\n<p>That single difference explains everything else. Amorphous PET is clear, tough, and softens at about 70 degrees, which is why an APET tray cannot go in an oven. CPET is opaque white, slightly less tough, and holds its shape at 220 degrees for an hour, which is why it can.<\/p>\n<p>The resin is not exotic: it is a sheet or film grade PET with a nucleating agent, sometimes with a crystallisation accelerator. The crystallisation is done on the thermoformer, in the mould, in the seconds between forming and ejection. There is no separate annealing step in a normal CPET line.<\/p>\n<p>The opacity is not a pigment. Crystallites are larger than the wavelength of visible light and scatter it. You cannot make a clear ovenable tray from PET, and a supplier who offers one is offering APET with a temperature claim it will not survive.<\/p>\n<h2 id=\"crystallinity\">Crystallinity is the whole trick<\/h2>\n<p>The relationship between mould temperature and crystallinity is not linear. It has a knee, and the knee is the entire process window.<\/p>\n<table>\n<thead>\n<tr>\n<th>Mould temperature, C<\/th>\n<th>Crystallinity, %<\/th>\n<th>Tray behaviour at 200 C<\/th>\n<\/tr>\n<\/thead>\n<tbody>\n<tr>\n<td>20<\/td>\n<td>3<\/td>\n<td>Slumps within seconds, no oven use<\/td>\n<\/tr>\n<tr>\n<td>60<\/td>\n<td>4<\/td>\n<td>Slumps, and blushes white on bending<\/td>\n<\/tr>\n<tr>\n<td>100<\/td>\n<td>8<\/td>\n<td>Sags visibly, dimensionally useless<\/td>\n<\/tr>\n<tr>\n<td>120<\/td>\n<td>18<\/td>\n<td>Survives a short reheat, warps at 200 C<\/td>\n<\/tr>\n<tr>\n<td>140<\/td>\n<td>31<\/td>\n<td>Ovenable, marginal at 220 C<\/td>\n<\/tr>\n<tr>\n<td>160<\/td>\n<td>38<\/td>\n<td>Ovenable, stable to 220 C for 60 minutes<\/td>\n<\/tr>\n<tr>\n<td>170<\/td>\n<td>39<\/td>\n<td>Ovenable, no further gain, longer cycle<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<p class=\"tablecap\">Table 1 - Crystallinity of a 0.8 mm PET sheet after 20 seconds in contact with a mould at the stated temperature, with a nucleated grade.<\/p>\n<p>Below 100 degrees the mould cools the sheet faster than the crystallites can grow, so the sheet quenches amorphous and stays clear. Between 100 and 140 the crystallisation rate rises faster than the cooling, and above 140 the sheet reaches 30 percent or more in a few seconds.<\/p>\n<p>Thirty percent is the number that matters because crystallites act as crosslinks. Below about 25 percent the amorphous phase between them still softens at 75 to 80 degrees and the tray sags under its own weight plus the food. Above 30 percent the crystalline network carries the load up to the melting range.<\/p>\n<p>Without a nucleating agent the same mould temperature gives roughly 15 percent and a tray that fails in the oven. This is why CPET is a grade, not a temperature setting: you cannot crystallise a standard bottle-grade PET on a thermoformer no matter how hot the mould is.<\/p>\n<h2 id=\"thermoform\">Forming: hot mould, slow cycle, and the shrink that comes with it<\/h2>\n<p>A CPET line is an APET line with a hot mould and a longer dwell. The sheet is heated to 120 to 160 degrees, which is above the glass transition at 78 and well below melting at 250, then formed and held against the mould until it is stiff enough to eject without distorting.<\/p>\n<table>\n<thead>\n<tr>\n<th>Mould temperature, C<\/th>\n<th>Cycle time, s<\/th>\n<th>Crystallinity, %<\/th>\n<th>Verdict<\/th>\n<\/tr>\n<\/thead>\n<tbody>\n<tr>\n<td>120<\/td>\n<td>4<\/td>\n<td>18<\/td>\n<td>Fast and useless<\/td>\n<\/tr>\n<tr>\n<td>130<\/td>\n<td>6<\/td>\n<td>22<\/td>\n<td>Still short of the limit<\/td>\n<\/tr>\n<tr>\n<td>140<\/td>\n<td>10<\/td>\n<td>31<\/td>\n<td>Minimum viable<\/td>\n<\/tr>\n<tr>\n<td>150<\/td>\n<td>16<\/td>\n<td>35<\/td>\n<td>Good balance<\/td>\n<\/tr>\n<tr>\n<td>160<\/td>\n<td>23<\/td>\n<td>38<\/td>\n<td>Standard production point<\/td>\n<\/tr>\n<tr>\n<td>170<\/td>\n<td>30<\/td>\n<td>39<\/td>\n<td>No gain for the time<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<p class=\"tablecap\">Table 2 - Cycle time for a 1 mm tray at each mould temperature, same pressure, same draw, same sheet.<\/p>\n<p>The trade-off is explicit and there is no way around it. 160 degrees gives an ovenable tray in 23 seconds; 120 degrees gives a tray in 4 seconds that will not survive a ready meal. The whole economics of a CPET line sit in that one column.<\/p>\n<p>Shrinkage is the second consequence. CPET shrinks 1.5 to 2.5 percent on forming, and a further 0.3 to 0.8 percent during the first oven cycle as the amorphous fraction finishes crystallising. The tool must be cut oversize for the first, and the customer must be told about the second, because a tray that no longer fits a lidding machine after its first use is a complaint, not a defect.<\/p>\n<h2 id=\"dual-ovenable\">Dual-ovenable: what the claim actually requires<\/h2>\n<p>Dual-ovenable means microwave and conventional oven, usually minus 40 to plus 220 degrees for 30 to 60 minutes. It is a claim about the finished pack, not about the material, and it has to be demonstrated on the worst case rather than the convenient one.<\/p>\n<ul>\n<li>Dimensional stability: the tray must not sag, distort or lose its seal at the top temperature for the full time.<\/li>\n<li>No blistering or delamination, which is what happens when residual moisture in the sheet flashes to steam.<\/li>\n<li>Overall migration within 10 mg\/dm2 under EU 10\/2011, and specific migration for the monomers and additives, at the temperature and time of use.<\/li>\n<li>FDA compliance under 21 CFR 177.1630 for PET, if the pack is sold in the United States.<\/li>\n<li>Microwave behaviour: no arcing, no hot spots, and a base that does not deform under a susceptor.<\/li>\n<\/ul>\n<p>The case that fails is not the dry pastry. It is a tomato and cheese ready meal at 220 degrees for 60 minutes, where the acidity, the fat and the water all attack the tray at once. Test that one, at the top of the tolerance, on the thinnest wall in the cavity.<\/p>\n<h2 id=\"defects\">Defects: blushing, warp and stress cracking<\/h2>\n<p>CPET has a short list of characteristic defects and each one points at a different part of the process.<\/p>\n<ul>\n<li>Blushing, white streaks or a milky patch: surface crystallinity from over-stretch or a locally cold mould. Raise the mould temperature, reduce the draw ratio, or add plug assist.<\/li>\n<li>Warp: differential crystallinity through the thickness, usually from a temperature difference between the male and female side. Balance both halves and cool symmetrically.<\/li>\n<li>Stress cracking at the corners: over-packing at the corner combined with a sharp radius. Radius of at least 3 mm, lower forming pressure, more pre-stretch.<\/li>\n<li>Sink in the base: uneven sheet temperature, so the base crystallises less than the wall. Fix the heater zoning and lengthen the soak.<\/li>\n<li>Delamination or bubbles: moisture in the sheet. PET hydrolyses above 0.005 percent water; dry the sheet and keep it dry before forming.<\/li>\n<\/ul>\n<p>The moisture point is worth its own sentence because it is invisible until it is not. A roll of PET sheet absorbs water from the air, and a roll that has been open in a humid plant for a week will blister in the oven even though it formed perfectly.<\/p>\n<h2 id=\"tooling\">Tooling: aluminium, hot, and cut oversize<\/h2>\n<p>CPET tools are usually aluminium, because heat transfer matters more than wear resistance and aluminium is cheap to cut and cheap to re-cut. Cartridge heaters or oil circuits hold the mould at 150 to 170 degrees, and the temperature uniformity across the cavity matters more than the absolute value.<\/p>\n<p>Cavitation is normally 1 to 8 for trays. The cycle is long, so cavitation pays back quickly, and a four-cavity tool on a 23 second cycle is a different business from a single-cavity tool on the same cycle.<\/p>\n<p>Cut the cavity oversize by the forming shrinkage, and then by the first-use shrinkage if the customer's filling line references the tray edge. A 200 mm tray needs a cavity of about 204 to 205 mm, and the exact figure is measured on the first tool rather than taken from a table.<\/p>\n<p>Venting deserves a note. PET needs generous venting at the end of fill, because trapped gas gives a burn mark or a short corner that looks like a forming problem and is actually a venting problem.<\/p>\n<h2 id=\"cost\">The cost is the cycle, and the value is the material<\/h2>\n<p>Twenty-three seconds against four seconds is the whole economics of CPET. A line running at 23 seconds needs nearly six times the machine hours of an APET line for the same output, and that is why CPET trays cost two to three times what an APET tray of the same weight costs.<\/p>\n<p>The saving is on the other side of the comparison. CPET replaces aluminium foil trays, which are heavier, cannot be microwaved, and have a higher carbon footprint per tray. It also replaces multi-material laminates that cannot be recycled. A mono-material PET tray that goes in both ovens and into the PET recycling stream is a strong proposition even at twice the piece price.<\/p>\n<div class=\"callout\">Do not compare CPET with APET on piece price. Compare it with the aluminium tray it replaces, including the oven, the microwave and the disposal, because that is the decision the customer is actually making.<\/div>\n<div class=\"faq\">\n<h3>Can a CPET tray go in a microwave?<\/h3>\n<p>Yes, and that is the point of it. CPET is one of very few materials that is genuinely dual-ovenable, and it does not arc or deform in a microwave the way a metallised tray does.<\/p>\n<h3>Why is CPET white and APET clear?<\/h3>\n<p>The crystallites scatter visible light. Amorphous PET has no crystallites and is clear; crystalline PET has spherulites larger than the wavelength of light and is opaque. There is no clear ovenable PET tray.<\/p>\n<h3>What is the maximum service temperature of a CPET tray?<\/h3>\n<p>220 degrees for 30 to 60 minutes, depending on the wall thickness and the food. The limit is not melting, it is the slow deformation of the remaining amorphous fraction under load.<\/p>\n<h3>Why does my tray warp in the oven but not on the line?<\/h3>\n<p>Under-crystallised, or a base that is thinner than the wall. The tray is dimensionally stable at room temperature with 20 percent crystallinity and fails at 200 degrees; check the crystallinity by DSC rather than by eye.<\/p>\n<h3>Can CPET be recycled?<\/h3>\n<p>Yes, in the PET stream, provided the tray is rinsed and the lidding film is removed. CPET and APET are the same polymer, and a recycler does not need to separate them.<\/p>\n<h3>Does CPET need a nucleating agent?<\/h3>\n<p>In practice yes. Without it the crystallisation rate is too slow for a 20 second cycle and the mould temperature needed to reach 30 percent is above what the sheet tolerates.<\/p>\n<\/div>\n<div class=\"cta\">\n<p class=\"cta-h\">Moving a ready meal from foil or APET to CPET?<\/p>\n<p>Send the tray drawing, the fill weight and the oven profile. We will tell you the crystallinity you need, the cycle time it costs, and whether the wall section will survive the corner radius you have drawn.<\/p>\n<p><a class=\"btn\" href=\"https:\/\/uplastech.com\/pt\/custom-vacuum-forming\/\">Talk to a thermoforming engineer<\/a>\n<\/div>\n<div class=\"rel\">\n<h4>Continue reading<\/h4>\n<ul>\n<li><a href=\"https:\/\/uplastech.com\/pt\/pet-rpet-thermoforming\/\">PET and RPET Thermoforming<\/a><\/li>\n<li><a href=\"https:\/\/uplastech.com\/pt\/food-contact-thermoforming-compliance\/\">Food Contact Thermoforming Compliance<\/a><\/li>\n<li><a href=\"https:\/\/uplastech.com\/pt\/thermoforming-sheet-heating-temperature-window\/\">Thermoforming Sheet Heating Temperature Window<\/a><\/li>\n<li><a href=\"https:\/\/uplastech.com\/pt\/pp-cup-thermoforming\/\">PP Cup Thermoforming<\/a><\/li>\n<li><a href=\"https:\/\/uplastech.com\/pt\/vacuum-forming-defects-troubleshooting\/\">Vacuum Forming Defects and Troubleshooting<\/a><\/li>\n<\/ul>\n<\/div>\n<\/div>","protected":false},"excerpt":{"rendered":"<p>CPET is ordinary PET formed against a hot mould. The heat that crystallises the sheet is what lets the tray survive 220 degrees, and it is paid for in cycle time, thirty seconds at a time.<\/p>","protected":false},"author":1,"featured_media":7824,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_seopress_titles_title":"CPET Ovenable Trays: Crystallinity and Cycle Time","_seopress_titles_desc":"CPET ovenable tray thermoforming: how crystallinity makes PET oven-safe, mould temperature and cycle time, shrinkage allowance, blushing, warp and the dual-oven","_seopress_robots_index":"","_seopress_robots_follow":"","_seopress_robots_imageindex":"","_seopress_robots_snippet":"","_seopress_robots_primary_cat":"29","_seopress_robots_breadcrumbs":"","_seopress_robots_freeze_modified_date":"","_seopress_robots_custom_modified_date":"","_seopress_robots_canonical":"","_seopress_social_fb_title":"","_seopress_social_fb_desc":"","_seopress_social_fb_img":"","_seopress_social_fb_img_attachment_id":0,"_seopress_social_fb_img_width":0,"_seopress_social_fb_img_height":0,"_seopress_social_twitter_title":"","_seopress_social_twitter_desc":"","_seopress_social_twitter_img":"","_seopress_social_twitter_img_attachment_id":0,"_seopress_social_twitter_img_width":0,"_seopress_social_twitter_img_height":0,"_seopress_redirections_value":"","_seopress_redirections_enabled":"","_seopress_redirections_enabled_regex":"","_seopress_redirections_logged_status":"","_seopress_redirections_param":"","_seopress_redirections_type":0,"_seopress_analysis_target_kw":"","footnotes":""},"categories":[29],"tags":[],"class_list":["post-7825","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-vacuum-forming"],"meta_box":{"post-to-quiz_to":[]},"_links":{"self":[{"href":"https:\/\/uplastech.com\/pt\/wp-json\/wp\/v2\/posts\/7825","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/uplastech.com\/pt\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/uplastech.com\/pt\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/uplastech.com\/pt\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/uplastech.com\/pt\/wp-json\/wp\/v2\/comments?post=7825"}],"version-history":[{"count":0,"href":"https:\/\/uplastech.com\/pt\/wp-json\/wp\/v2\/posts\/7825\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/uplastech.com\/pt\/wp-json\/wp\/v2\/media\/7824"}],"wp:attachment":[{"href":"https:\/\/uplastech.com\/pt\/wp-json\/wp\/v2\/media?parent=7825"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/uplastech.com\/pt\/wp-json\/wp\/v2\/categories?post=7825"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/uplastech.com\/pt\/wp-json\/wp\/v2\/tags?post=7825"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}