{"id":7606,"date":"2026-10-27T01:14:27","date_gmt":"2026-10-27T01:14:27","guid":{"rendered":"https:\/\/uplastech.com\/pc-injection-molding-guide\/"},"modified":"2026-10-27T01:14:27","modified_gmt":"2026-10-27T01:14:27","slug":"pc-injection-molding-guide","status":"publish","type":"post","link":"https:\/\/uplastech.com\/fr\/pc-injection-molding-guide\/","title":{"rendered":"PC Injection Molding: Drying, Melt Temperature and Stress Cracking"},"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 \u81ea\u52a8\u5c55\u5f00\u7684\u95ee\u5019\u5361\uff0c\u53ea\u4fdd\u7559\u5706\u5f62\u6c14\u6ce1\uff0c\u907f\u514d\u906e\u6321\u4fa7\u680f\u8be2\u76d8\u63d0\u4ea4\u6309\u94ae *\/\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\/im-pc-part.jpg\" alt=\"Clear polycarbonate injection moulded lens cover and an opaque black PC bracket on an inspection bench\" width=\"1536\" height=\"909\"><figcaption>A clear PC cover and a glass-filled black PC bracket from the same family of grades. The transparent part is where every PC problem becomes visible at once: flow marks, stress, and any moisture the dryer missed.<\/figcaption><\/figure>\n<div class=\"toc\"><\/div>\n<h2 id=\"why\">Why PC is difficult, and why it is worth it<\/h2>\n<p>Polycarbonate has an unusual combination: it is transparent, it has an impact strength of 600 \u2013 900 J\/m notched, it holds its properties to 120 \u00b0C, and it is dimensionally stable. Nothing else in the commodity engineering range does all four. That is why it is used for machine guards, lenses, medical housings, electrical enclosures and power-tool bodies.<\/p>\n<p>The price of that combination is a narrow processing window and two failure modes that are unforgiving. PC must be dried to below 0.02 % moisture \u2014 one of the tightest limits of any common polymer \u2014 and it must be moulded with low residual stress, because polycarbonate stress-cracks in contact with almost every solvent it meets, including some mould releases, some adhesives, and some cleaning agents.<\/p>\n<div class=\"callout\">\n<p><strong>The two numbers that decide whether a PC job runs:<\/strong> moisture below <strong>0.02 %<\/strong> at the hopper, and residual stress low enough to survive a 30-second immersion in carbon tetrachloride or a suitable stress-crack test. Get both right and PC is straightforward. Get either wrong and you will spend weeks chasing a defect that is not where it appears.<\/p>\n<\/div>\n<h2 id=\"grades\">Grades<\/h2>\n<table>\n<thead>\n<tr>\n<th>Grade family<\/th>\n<th>Key property<\/th>\n<th>MFR (g\/10 min)<\/th>\n<th>Used for<\/th>\n<\/tr>\n<\/thead>\n<tbody>\n<tr>\n<td>Optical \/ lens<\/td>\n<td>Haze &lt; 1 %, low birefringence<\/td>\n<td>6 \u2013 15<\/td>\n<td>Lenses, light covers, display windows<\/td>\n<\/tr>\n<tr>\n<td>General purpose<\/td>\n<td>Balanced clarity and flow<\/td>\n<td>10 \u2013 22<\/td>\n<td>Housings, guards<\/td>\n<\/tr>\n<tr>\n<td>High flow<\/td>\n<td>Thin walls, long flow<\/td>\n<td>22 \u2013 40<\/td>\n<td>Thin-wall electrical parts<\/td>\n<\/tr>\n<tr>\n<td>Flame retardant<\/td>\n<td>UL94 V-0 at 1.5 mm<\/td>\n<td>8 \u2013 20<\/td>\n<td>Power supplies, chargers<\/td>\n<\/tr>\n<tr>\n<td>UV stabilised<\/td>\n<td>Retains clarity outdoors<\/td>\n<td>8 \u2013 18<\/td>\n<td>Outdoor lenses, signage<\/td>\n<\/tr>\n<tr>\n<td>Scratch resistant (hard coat)<\/td>\n<td>Surface hardness 2 \u2013 3 H<\/td>\n<td>8 \u2013 15<\/td>\n<td>Touch screens, displays<\/td>\n<\/tr>\n<tr>\n<td>Glass filled, 10 \u2013 30 %<\/td>\n<td>Modulus 6 \u2013 10 GPa<\/td>\n<td>5 \u2013 15<\/td>\n<td>Structural brackets<\/td>\n<\/tr>\n<tr>\n<td>PC\/ABS blend<\/td>\n<td>Better flow, lower cost<\/td>\n<td>10 \u2013 25<\/td>\n<td>Housings where clarity is not needed<\/td>\n<\/tr>\n<tr>\n<td>Medical \/ ISO 10993<\/td>\n<td>Biocompatibilit\u00e9<\/td>\n<td>8 \u2013 20<\/td>\n<td>Device housings, fluid paths<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<p class=\"tablecap\">Table 1 \u2014 PC grade families. Optical grades are a separate specification, not a premium version of general purpose.<\/p>\n<h2 id=\"drying\">Drying: the non-negotiable step<\/h2>\n<p>Polycarbonate hydrolyses. Water at moulding temperature breaks the carbonate linkage, reducing molecular weight permanently. A single wet shot does not just produce a cosmetic defect \u2014 it degrades the material, and the part that comes out has lower impact strength even after the streaks are gone.<\/p>\n<table>\n<thead>\n<tr>\n<th>Moisture content<\/th>\n<th>Visual result<\/th>\n<th>Impact retention<\/th>\n<\/tr>\n<\/thead>\n<tbody>\n<tr>\n<td>&lt; 0.015 %<\/td>\n<td>Clear, no streaks<\/td>\n<td>100 %<\/td>\n<\/tr>\n<tr>\n<td>0.02 %<\/td>\n<td>Clear on most parts<\/td>\n<td>95 \u2013 100 %<\/td>\n<\/tr>\n<tr>\n<td>0.03 %<\/td>\n<td>Faint silver streaking near the gate<\/td>\n<td>85 \u2013 95 %<\/td>\n<\/tr>\n<tr>\n<td>0.05 %<\/td>\n<td>Visible streaks across the part<\/td>\n<td>70 \u2013 85 %<\/td>\n<\/tr>\n<tr>\n<td>0.10 %<\/td>\n<td>Bubbles, splay, cloudy patches<\/td>\n<td>50 \u2013 70 %<\/td>\n<\/tr>\n<tr>\n<td>0.20 %<\/td>\n<td>Gross foaming, unusable<\/td>\n<td>&lt; 40 %<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<p class=\"tablecap\">Table 2 \u2014 PC moisture versus outcome. The impact loss is permanent and invisible.<\/p>\n<table>\n<thead>\n<tr>\n<th>Dryer type<\/th>\n<th>Temp\u00e9rature<\/th>\n<th>Time<\/th>\n<th>Notes<\/th>\n<\/tr>\n<\/thead>\n<tbody>\n<tr>\n<td>Desiccant wheel (recommended)<\/td>\n<td>120 \u00b0C<\/td>\n<td>3 \u2013 4 h<\/td>\n<td>Dew point \u221220 \u00b0C or lower; the standard for PC<\/td>\n<\/tr>\n<tr>\n<td>Vacuum dryer<\/td>\n<td>110 \u2013 120 \u00b0C<\/td>\n<td>1.5 \u2013 2.5 h<\/td>\n<td>Faster; good for small batches<\/td>\n<\/tr>\n<tr>\n<td>Hot air oven<\/td>\n<td>120 \u00b0C<\/td>\n<td>4 \u2013 6 h<\/td>\n<td>Only if the air is genuinely dry; ambient humidity re-wets the resin<\/td>\n<\/tr>\n<tr>\n<td>Hopper dryer, short<\/td>\n<td>120 \u00b0C<\/td>\n<td>2 h minimum<\/td>\n<td>Not sufficient for a cold-start; only for holding dried resin<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<p class=\"tablecap\">Table 3 \u2014 Drying routes. A hot-air oven in a humid climate can plateau at 0.05 % and never get lower.<\/p>\n<div class=\"myth\">\n<p><b>Myth: \"the streaks disappeared after an hour, so it's fine now.\"<\/b> Silver streaks disappear when the surface moisture drops below about 0.03 %. The molecular weight damage from the first wet shots remains in the barrel until it is purged, and the parts made in that period have reduced impact. Purge and restart after a moisture event \u2014 do not just wait for the streaks to go.<\/p>\n<\/div>\n<h2 id=\"processing\">The processing window<\/h2>\n<table>\n<thead>\n<tr>\n<th>Param\u00e8tres<\/th>\n<th>Typical setting<\/th>\n<th>Notes<\/th>\n<\/tr>\n<\/thead>\n<tbody>\n<tr>\n<td>Temp\u00e9rature de fusion<\/td>\n<td>280 \u2013 310 \u00b0C<\/td>\n<td>Below 270: unmelt and high stress. Above 320: degradation and yellowing<\/td>\n<\/tr>\n<tr>\n<td>Barrel profile<\/td>\n<td>260 \/ 280 \/ 295 \/ 300 \u00b0C<\/td>\n<td>Feed zone cool to avoid bridging<\/td>\n<\/tr>\n<tr>\n<td>Nozzle<\/td>\n<td>290 \u2013 300 \u00b0C<\/td>\n<td>Use a reverse-taper or free-flow nozzle<\/td>\n<\/tr>\n<tr>\n<td>Mould temperature<\/td>\n<td>80 \u2013 110 \u00b0C<\/td>\n<td>The single biggest lever on stress and surface<\/td>\n<\/tr>\n<tr>\n<td>Injection pressure<\/td>\n<td>80 \u2013 140 MPa<\/td>\n<td>High viscosity; expect high pressures<\/td>\n<\/tr>\n<tr>\n<td>Injection speed<\/td>\n<td>Moderate to fast<\/td>\n<td>Fast fill reduces stress but can cause jetting<\/td>\n<\/tr>\n<tr>\n<td>Hold pressure<\/td>\n<td>50 \u2013 70 % of injection<\/td>\n<td>Long hold; PC packs slowly<\/td>\n<\/tr>\n<tr>\n<td>Back pressure<\/td>\n<td>0.5 \u2013 1.5 MPa<\/td>\n<td>Helps homogenise; watch for over-heating<\/td>\n<\/tr>\n<tr>\n<td>Vitesse de la vis<\/td>\n<td>40 \u2013 70 rpm<\/td>\n<td>Low peripheral speed<\/td>\n<\/tr>\n<tr>\n<td>Residence time<\/td>\n<td>&lt; 8 min<\/td>\n<td>Long residence at 300 \u00b0C yellows the melt<\/td>\n<\/tr>\n<tr>\n<td>Regrind<\/td>\n<td>0 \u2013 20 %<\/td>\n<td>Must be dried again; each pass reduces molecular weight<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<p class=\"tablecap\">Table 4 \u2014 A starting window for optical-grade PC. Confirm against the grade datasheet.<\/p>\n<p>Mould temperature is where most PC problems are solved or created. At 60 \u00b0C a PC part looks fine and is full of frozen-in stress: it will craze around inserts, crack when assembled, and fail a solvent test. At 90 \u2013 100 \u00b0C the surface replicates better, the stress relaxes before the part ejects, and the cycle is longer but the yield is far higher. The extra 10 seconds per shot is almost always cheaper than the sorting.<\/p>\n<h2 id=\"stress\">Residual stress: how to see it and how to remove it<\/h2>\n<table>\n<thead>\n<tr>\n<th>Test<\/th>\n<th>M\u00e9thode<\/th>\n<th>Pass criterion<\/th>\n<\/tr>\n<\/thead>\n<tbody>\n<tr>\n<td>Solvent immersion<\/td>\n<td>Carbon tetrachloride or a proprietary stress-crack reagent, 30 s to 3 min<\/td>\n<td>No crazing within 60 s<\/td>\n<\/tr>\n<tr>\n<td>Solvent wipe<\/td>\n<td>Wipe with acetone or ethyl acetate, leave 5 min<\/td>\n<td>No crazing<\/td>\n<\/tr>\n<tr>\n<td>Polarised light<\/td>\n<td>View between crossed polarisers<\/td>\n<td>Uniform low-order colour; strong bands indicate stress<\/td>\n<\/tr>\n<tr>\n<td>Heat relaxation<\/td>\n<td>Measure, hold at 120 \u00b0C for 1 h, re-measure<\/td>\n<td>Dimensional change &lt; 0.2 %<\/td>\n<\/tr>\n<tr>\n<td>Assembly test<\/td>\n<td>Torque the screw to specification, hold 24 h<\/td>\n<td>No cracking at the boss<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<p class=\"tablecap\">Table 5 \u2014 PC stress tests. The solvent immersion test is the industry standard and takes one minute.<\/p>\n<p>Annealing removes stress after the fact and is standard practice for machined or heavily loaded PC parts. For moulded parts it is a band-aid: the right fix is a hotter mould, a slower fill and better packing.<\/p>\n<table>\n<thead>\n<tr>\n<th>Annealing schedule<\/th>\n<th>Temp\u00e9rature<\/th>\n<th>Time<\/th>\n<\/tr>\n<\/thead>\n<tbody>\n<tr>\n<td>Thin parts, &lt; 2 mm<\/td>\n<td>120 \u00b0C<\/td>\n<td>1 h<\/td>\n<\/tr>\n<tr>\n<td>2 \u2013 4 mm<\/td>\n<td>120 \u00b0C<\/td>\n<td>2 h<\/td>\n<\/tr>\n<tr>\n<td>4 \u2013 8 mm<\/td>\n<td>120 \u00b0C<\/td>\n<td>3 \u2013 4 h<\/td>\n<\/tr>\n<tr>\n<td>Glass filled<\/td>\n<td>125 \u00b0C<\/td>\n<td>2 \u2013 4 h<\/td>\n<\/tr>\n<tr>\n<td>Cool-down rate<\/td>\n<td>\u2014<\/td>\n<td>\u2264 10 \u00b0C\/h to avoid re-introducing stress<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<p class=\"tablecap\">Table 6 \u2014 Annealing. Slow cooling matters as much as the hold time.<\/p>\n<h2 id=\"design\">Design rules<\/h2>\n<table>\n<thead>\n<tr>\n<th>Fonctionnalit\u00e9<\/th>\n<th>Rule<\/th>\n<th>Why PC is different<\/th>\n<\/tr>\n<\/thead>\n<tbody>\n<tr>\n<td>Wall thickness<\/td>\n<td>2.0 \u2013 3.5 mm; avoid &lt; 1.5 mm<\/td>\n<td>High viscosity makes thin walls hard to fill<\/td>\n<\/tr>\n<tr>\n<td>Wall uniformity<\/td>\n<td>Within 20 %<\/td>\n<td>Thick sections cause voids and stress<\/td>\n<\/tr>\n<tr>\n<td>Internal radius<\/td>\n<td>\u2265 0.5 \u00d7 wall, preferably 1.0 \u00d7<\/td>\n<td>PC is notch sensitive \u2014 sharp corners are crack starters<\/td>\n<\/tr>\n<tr>\n<td>Draft<\/td>\n<td>1.5\u00b0 minimum<\/td>\n<td>High shrinkage force; parts grip the core<\/td>\n<\/tr>\n<tr>\n<td>Gate<\/td>\n<td>Large, edge or direct; avoid small pin gates<\/td>\n<td>High shear degrades PC at the gate<\/td>\n<\/tr>\n<tr>\n<td>Metal inserts<\/td>\n<td>Design for 0.3 \u2013 0.5 % differential expansion<\/td>\n<td>PC expands 65 \u2013 70 \u00d7 10\u207b\u2076\/K vs 23 for aluminium<\/td>\n<\/tr>\n<tr>\n<td>Threads<\/td>\n<td>Moulded threads only in low-stress areas<\/td>\n<td>Thread roots are stress concentrators<\/td>\n<\/tr>\n<tr>\n<td>Snap fits<\/td>\n<td>Strain \u2264 1.0 % for repeated flexing<\/td>\n<td>PC tolerates a single snap better than repeated<\/td>\n<\/tr>\n<tr>\n<td>Sharp edges<\/td>\n<td>Break all external edges 0.3 mm<\/td>\n<td>Handling damage becomes a crack<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<p class=\"tablecap\">Table 7 \u2014 PC design rules. Notch sensitivity is the theme.<\/p>\n<h2 id=\"optical\">Optical parts: the extra requirements<\/h2>\n<p>A lens or a light guide is a different specification from a housing, and the differences are not obvious from a datasheet.<\/p>\n<table>\n<thead>\n<tr>\n<th>Requirement<\/th>\n<th>What it needs<\/th>\n<th>If it is missed<\/th>\n<\/tr>\n<\/thead>\n<tbody>\n<tr>\n<td>Tool polish<\/td>\n<td>SPI A-1 or A-2, diamond polish<\/td>\n<td>Every tool mark is visible in the transmitted light<\/td>\n<\/tr>\n<tr>\n<td>Gate location<\/td>\n<td>Outside the optical aperture<\/td>\n<td>Gate mark and flow lines in the field of view<\/td>\n<\/tr>\n<tr>\n<td>Flow front<\/td>\n<td>Single, uninterrupted front<\/td>\n<td>Weld lines visible as a bright or dark line<\/td>\n<\/tr>\n<tr>\n<td>Mould temperature<\/td>\n<td>100 \u2013 120 \u00b0C<\/td>\n<td>Flow marks and internal stress birefringence<\/td>\n<\/tr>\n<tr>\n<td>Material grade<\/td>\n<td>Optical grade, low birefringence<\/td>\n<td>Rainbow patterns in polarised light<\/td>\n<\/tr>\n<tr>\n<td>Drying<\/td>\n<td>0.01 % or better<\/td>\n<td>Micro-bubbles that scatter light<\/td>\n<\/tr>\n<tr>\n<td>Packing<\/td>\n<td>Low hold pressure, slow<\/td>\n<td>Orientation and birefringence at the gate<\/td>\n<\/tr>\n<tr>\n<td>Handling<\/td>\n<td>No contact with the optical surface<\/td>\n<td>Scratches that cannot be polished out<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<p class=\"tablecap\">Table 8 \u2014 Optical PC requirements. Birefringence is the one that is invisible until the part is between polarisers.<\/p>\n<h2 id=\"defects\">Defects and causes<\/h2>\n<table>\n<thead>\n<tr>\n<th>D\u00e9faut<\/th>\n<th>Cause<\/th>\n<th>Fix<\/th>\n<\/tr>\n<\/thead>\n<tbody>\n<tr>\n<td>Silver streaks \/ splay<\/td>\n<td>Moisture<\/td>\n<td>Dry to 0.02 %; check dew point and hopper seal<\/td>\n<\/tr>\n<tr>\n<td>Crazing after assembly<\/td>\n<td>Residual stress plus solvent or stress<\/td>\n<td>Raise mould temperature; anneal; check assembly torque<\/td>\n<\/tr>\n<tr>\n<td>Yellowing<\/td>\n<td>Over-temperature or long residence<\/td>\n<td>Lower melt 10 \u00b0C; reduce shot-to-barrel ratio<\/td>\n<\/tr>\n<tr>\n<td>Flow marks on clear parts<\/td>\n<td>Cold mould or slow fill<\/td>\n<td>Mould to 100 \u00b0C; increase injection speed<\/td>\n<\/tr>\n<tr>\n<td>Bubbles in thick sections<\/td>\n<td>Voids from shrinkage, or moisture<\/td>\n<td>Increase hold pressure and time; dry<\/td>\n<\/tr>\n<tr>\n<td>Weld line visible<\/td>\n<td>Low mould temperature, slow front<\/td>\n<td>Raise mould; raise speed through the weld<\/td>\n<\/tr>\n<tr>\n<td>Crack at the gate<\/td>\n<td>High shear, small gate<\/td>\n<td>Enlarge the gate; slow the first stage<\/td>\n<\/tr>\n<tr>\n<td>Cloudy patches<\/td>\n<td>Moisture or degraded material<\/td>\n<td>Dry; purge; check for dead spots in the hot runner<\/td>\n<\/tr>\n<tr>\n<td>Black specks<\/td>\n<td>Carbonised material in the hot runner or nozzle<\/td>\n<td>Purge with PC purge compound; inspect hot-runner tips<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<p class=\"tablecap\">Table 9 \u2014 PC defects. Note that four of the nine trace back to moisture or residence time.<\/p>\n<h2 id=\"flow\">Flow length, wall thickness and the pressure ceiling<\/h2>\n<p>PC has high melt viscosity, which limits how far it can flow through a thin wall before the pressure runs out. This is the constraint that most often forces a design change, and it is worth checking before the tool is cut.<\/p>\n<table>\n<thead>\n<tr>\n<th>Wall thickness<\/th>\n<th>Practical flow length (unfilled PC)<\/th>\n<th>Flow ratio<\/th>\n<\/tr>\n<\/thead>\n<tbody>\n<tr>\n<td>1.0 mm<\/td>\n<td>70 \u2013 90 mm<\/td>\n<td>70 \u2013 90 : 1<\/td>\n<\/tr>\n<tr>\n<td>1.5 mm<\/td>\n<td>130 \u2013 170 mm<\/td>\n<td>85 \u2013 115 : 1<\/td>\n<\/tr>\n<tr>\n<td>2.0 mm<\/td>\n<td>200 \u2013 260 mm<\/td>\n<td>100 \u2013 130 : 1<\/td>\n<\/tr>\n<tr>\n<td>2.5 mm<\/td>\n<td>280 \u2013 360 mm<\/td>\n<td>110 \u2013 145 : 1<\/td>\n<\/tr>\n<tr>\n<td>3.0 mm<\/td>\n<td>360 \u2013 450 mm<\/td>\n<td>120 \u2013 150 : 1<\/td>\n<\/tr>\n<tr>\n<td>4.0 mm<\/td>\n<td>480 \u2013 600 mm<\/td>\n<td>120 \u2013 150 : 1<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<p class=\"tablecap\">Table 9 \u2014 Flow length for unfilled PC at 300 \u00b0C melt and 100 \u00b0C mould. Glass-filled grades reach 60 \u2013 75 % of these figures.<\/p>\n<p>If the required flow length exceeds the table, you have four options: thicken the wall, add a gate in the middle, raise the melt temperature (limited by degradation), or change material. Adding a second gate is often the cheapest, but it creates a weld line \u2014 which on a transparent part is a visible defect and must be placed outside the optical area.<\/p>\n<div class=\"callout\">\n<p><strong>The wall-thickness trap:<\/strong> designers often thin a PC wall to save material and cycle time, then find the part will not fill. Going from 2.5 mm to 2.0 mm cuts the part volume by 20 % but cuts the flow length by nearly 30 % and raises the required injection pressure by 50 \u2013 70 %. On PC the two effects usually cancel out and the part fails to fill at the pressure limit.<\/p>\n<\/div>\n<h2 id=\"medical\">Medical and food-contact PC<\/h2>\n<p>Polycarbonate is widely used in medical devices, and the qualification requirements are specific.<\/p>\n<table>\n<thead>\n<tr>\n<th>Requirement<\/th>\n<th>What it means<\/th>\n<th>Watch out for<\/th>\n<\/tr>\n<\/thead>\n<tbody>\n<tr>\n<td>ISO 10993<\/td>\n<td>Biocompatibility for the intended contact duration<\/td>\n<td>The grade, not the polymer, is qualified<\/td>\n<\/tr>\n<tr>\n<td>USP Class VI<\/td>\n<td>Biological reactivity<\/td>\n<td>Often quoted instead of ISO 10993 \u2014 they are not equivalent<\/td>\n<\/tr>\n<tr>\n<td>Gamma sterilisation<\/td>\n<td>25 \u2013 50 kGy<\/td>\n<td>PC yellows slightly; specify a gamma-stable grade<\/td>\n<\/tr>\n<tr>\n<td>EtO sterilisation<\/td>\n<td>Ethylene oxide<\/td>\n<td>Requires aeration time; PC absorbs EtO<\/td>\n<\/tr>\n<tr>\n<td>Autoclave<\/td>\n<td>121 \u2013 134 \u00b0C steam<\/td>\n<td>PC is marginal \u2014 20 \u2013 50 cycles before crazing<\/td>\n<\/tr>\n<tr>\n<td>Food contact, EU<\/td>\n<td>EU 10\/2011<\/td>\n<td>BPA migration limits apply; check the grade's declaration<\/td>\n<\/tr>\n<tr>\n<td>Food contact, US<\/td>\n<td>FDA 21 CFR 177.1580<\/td>\n<td>Grade-specific<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<p class=\"tablecap\">Table 10 \u2014 PC medical and food qualification. Autoclave is the requirement that usually rules PC out.<\/p>\n<p>The BPA point is worth stating plainly: polycarbonate is made from bisphenol A, and BPA is restricted in food-contact applications for infants in the EU and has been voluntarily withdrawn from baby bottles in many markets. For food-contact PC in any infant-related application, expect a regulatory conversation. For medical device housings and industrial lenses, PC remains standard.<\/p>\n<h2 id=\"inspection\">Inspecting a transparent part<\/h2>\n<table>\n<thead>\n<tr>\n<th>D\u00e9faut<\/th>\n<th>How to see it<\/th>\n<th>Accept \/ reject basis<\/th>\n<\/tr>\n<\/thead>\n<tbody>\n<tr>\n<td>Flow marks<\/td>\n<td>Hold at an angle to a light source<\/td>\n<td>Any visible mark in the optical aperture is a reject<\/td>\n<\/tr>\n<tr>\n<td>Weld line<\/td>\n<td>Backlight, viewed through the part<\/td>\n<td>Reject in the aperture; acceptable outside<\/td>\n<\/tr>\n<tr>\n<td>Birefringence<\/td>\n<td>Crossed polarisers<\/td>\n<td>Compare against a limit sample<\/td>\n<\/tr>\n<tr>\n<td>Micro-bubbles<\/td>\n<td>10\u00d7 loupe under raking light<\/td>\n<td>Any bubble in the aperture is a reject<\/td>\n<\/tr>\n<tr>\n<td>Gate mark<\/td>\n<td>Direct inspection<\/td>\n<td>Outside the aperture by design<\/td>\n<\/tr>\n<tr>\n<td>Scratches<\/td>\n<td>Raking light<\/td>\n<td>Handling damage \u2014 reject<\/td>\n<\/tr>\n<tr>\n<td>Haze<\/td>\n<td>Haze meter<\/td>\n<td>Per the drawing; typically &lt; 1 % for optical<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<p class=\"tablecap\">Table 11 \u2014 Transparent part inspection. Crossed polarisers are the only way to see birefringence.<\/p>\n<p>Note that three of these checks need equipment that a general inspection bench does not have: polarisers, a haze meter and a controlled light source. A supplier who says they can mould optical PC should be able to show you all three.<\/p>\n<h2 id=\"faq\">Frequently asked questions<\/h2>\n<div class=\"faq\">\n<h3>Can PC be moulded without a desiccant dryer?<\/h3>\n<p>Not reliably. PC needs 120 \u00b0C of dry air at a dew point of \u221220 \u00b0C or better. A hot-air oven in a humid factory stabilises around 0.05 \u2013 0.1 %, which produces streaked, weakened parts. If you do not have a desiccant dryer, you cannot run PC.<\/p>\n<h3>Why does my PC part crack a week after moulding?<\/h3>\n<p>Residual stress plus a solvent. The two usual solvents are a mould release agent (silicone or a solvent carrier) and an assembly adhesive or cleaning fluid. Stress cracking is delayed because the solvent needs time to diffuse. Run the solvent immersion test on a moulded part \u2014 if it crazes within 60 seconds, the moulding is over-stressed.<\/p>\n<h3>What is the maximum wall thickness for PC?<\/h3>\n<p>Practically 4 \u2013 5 mm. Beyond that, the core stays molten while the skin freezes and you get voids and internal stress that annealing will not fully remove. For thick sections, consider a different material or a two-piece design.<\/p>\n<h3>Can PC be ultrasonically welded?<\/h3>\n<p>Yes, but it needs more energy than ABS and the joint design matters more. Amorphous PC welds well with a step joint and a generous energy director. Glass-filled PC is much harder \u2014 the fibres interfere with the melt at the interface.<\/p>\n<h3>How much does PC shrink?<\/h3>\n<p>0.5 \u2013 0.7 % for unfilled, 0.2 \u2013 0.5 % for 20 \u2013 30 % glass filled. The unfilled figure is more sensitive to mould temperature and wall thickness than ABS, so the tool needs to be corrected against parts moulded at production conditions, not at a trial setting.<\/p>\n<h3>Is PC suitable for outdoor use?<\/h3>\n<p>Standard PC yellows under UV within 1 \u2013 2 years. UV-stabilised grades with a coextruded or coated UV cap last 5 \u2013 10 years. For anything with a service life requirement outdoors, specify the UV grade and consider a hard coat as well.<\/p>\n<h3>What causes a cloudy patch on a clear PC part?<\/h3>\n<p>Usually moisture that was trapped in a slow-filling area, or degraded material from a hot-runner dead spot. If the cloudiness is always in the same place, suspect the hot runner; if it moves, suspect moisture.<\/p>\n<h3>PC or PMMA for a lens?<\/h3>\n<p>PMMA has better optical clarity and UV resistance and is cheaper; PC has 10 \u2013 20\u00d7 the impact strength and better heat resistance. For a lens that will be dropped, PC. For a lens that must be optically perfect and will be treated carefully, PMMA. For a lens that must do both, PC with a hard coat.<\/p>\n<\/div>\n<div class=\"cta\">\n<p class=\"cta-h\">Moulding a PC part and fighting stress or clarity?<\/p>\n<p>Send the drawing and the failure mode. We will tell you whether it is a drying problem, a mould-temperature problem or a design problem \u2014 and which of the three is cheapest to fix.<\/p>\n<p><a class=\"btn\" href=\"https:\/\/uplastech.com\/fr\/pc-injection-molding\/\">Talk to a PC moulding engineer<\/a>\n<\/div>\n<div class=\"rel\">\n<h4>Continue reading<\/h4>\n<ul>\n<li><a href=\"https:\/\/uplastech.com\/fr\/abs-injection-molding-guide\/\">ABS Injection Molding: Grades, Processing and Finishing<\/a><\/li>\n<li><a href=\"https:\/\/uplastech.com\/fr\/injection-molding-material-selection\/\">Injection Molding Material Selection: 14 Plastics Compared<\/a><\/li>\n<li><a href=\"https:\/\/uplastech.com\/fr\/injection-molding-tolerances\/\">Injection Molding Tolerances: What Is Actually Achievable<\/a><\/li>\n<li><a href=\"https:\/\/uplastech.com\/fr\/injection-molding-defects\/\">Injection Molding Defects: 12 Problems, Causes and Fixes<\/a><\/li>\n<li><a href=\"https:\/\/uplastech.com\/fr\/custom-injection-molding-guide\/\">Custom Injection Molding Guide: Process, Cost &amp; Tolerances<\/a><\/li>\n<\/ul>\n<\/div>\n<\/div>","protected":false},"excerpt":{"rendered":"<p>Polycarbonate moulding: why 0.02 % moisture is the limit, the processing window, residual stress tests, flow length limits, optical part requirements and medical qualification.<\/p>","protected":false},"author":1,"featured_media":7598,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"_seopress_titles_title":"PC Injection Molding: Drying, Melt Temperature & Stress","_seopress_titles_desc":"Polycarbonate moulding: the 0.02 % moisture limit, the processing window, residual stress tests, flow length limits and optical part requirements.","_seopress_robots_index":"1","_seopress_robots_follow":"1","_seopress_robots_imageindex":"","_seopress_robots_snippet":"","_seopress_robots_primary_cat":"35","_seopress_robots_breadcrumbs":"","_seopress_robots_freeze_modified_date":"","_seopress_robots_custom_modified_date":"","_seopress_robots_canonical":"https:\/\/uplastech.com\/pc-injection-molding-guide\/","_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":"pc injection molding","footnotes":""},"categories":[35],"tags":[],"class_list":["post-7606","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-injection-molding"],"meta_box":{"post-to-quiz_to":[]},"_links":{"self":[{"href":"https:\/\/uplastech.com\/fr\/wp-json\/wp\/v2\/posts\/7606","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/uplastech.com\/fr\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/uplastech.com\/fr\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/uplastech.com\/fr\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/uplastech.com\/fr\/wp-json\/wp\/v2\/comments?post=7606"}],"version-history":[{"count":0,"href":"https:\/\/uplastech.com\/fr\/wp-json\/wp\/v2\/posts\/7606\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/uplastech.com\/fr\/wp-json\/wp\/v2\/media\/7598"}],"wp:attachment":[{"href":"https:\/\/uplastech.com\/fr\/wp-json\/wp\/v2\/media?parent=7606"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/uplastech.com\/fr\/wp-json\/wp\/v2\/categories?post=7606"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/uplastech.com\/fr\/wp-json\/wp\/v2\/tags?post=7606"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}