门窗型材共挤用耐候PP+ASA，关键不在"哪种料好"，在表层管 UV 与外观、芯层管刚性尺寸与成本。这篇把共挤双层结构、三条衰退路径、五项判据、验证顺序与换料风险讲清，并说明哪三种情况这个件不该用改性PP 硬撑。
- 对照：贸易版《耐候PP 怎么选》（PP-M7，配方视角，本篇刻意不重复其主线）
"门窗型材表面一层白粉，手一擦就掉，颜色也淡了——这是改性PP 共挤料最常被人拿来问的一类失效。"
先别急着换料。看一眼粉化是集中在朝南那面还是整体均匀，再问一句"这个件当初是按共挤双层设计的，还是单层耐候PP 硬扛"——同一批料，两种情况结论完全不同。
一、户外门窗型材，单层耐候PP扛不住三条衰退路径
户外门窗型材不能只靠单层耐候PP 扛紫外——纯 PP 会沿粉化、褪色、脆化三条路径同时衰退，加助剂只能延后，改不了方向。
纯 PP 型材用在户外，耐候责任不能只压在一层料上。它会沿三条路径同时衰退：粉化（表面降解起白霜）、褪色（色差 ΔE 上升）、脆化（冲击强度衰减）。加 UV 助剂只能延后，改不了方向。
结论要先讲清：户外长寿命件，耐候是"设计"出来的，不是"加一种助剂"加出来的。共挤的做法，是把耐候责任整个交给表层。
一个内行细节：PP 主链上的叔碳氢键能低，比 PE 更容易被紫外夺氢引发断链。所以同一户外环境，PP 比 PE 老得快是结构性的——这不是配方水平问题，是基材起点差异。表层用本征耐候的 ASA，等于把这条起点差异在表层补回来。
二、门窗型材工况六维拆解：四个维度必须给数字
共挤门窗型材的工况，先把六维拆开，至少四个维度要落到具体数字，方向才定得下来。
| 维度 | 这个件的真实工况 | 对材料的要求 |
|---|
| 温度 | 户外 −20℃ 到 60℃；朝南无遮挡、受日晒的局部更高；温度循环 −20℃↔60℃ | 低温不脆、热不软、循环不变形 |
| 载荷 | 风压、启闭疲劳、装配约束；长期风载与自重 | 刚性够、蠕变小 |
| 介质 | 雨、紫外、盐雾、洗窗剂 | 耐候 + 耐化学 |
| 寿命 | 设计寿命常见 10-25 年，按暴露等级分档 | 长期老化后性能不塌 |
| 外观 | 色差 ΔE≤3.0（氙灯老化后）、表面无粉化 | 颜色与光泽稳定 |
| 合规 | 可参照建筑型材类老化与尺寸标准（如 EN 513:2018、GB/T 8814 类）做评价 | 按使用地区定 |
六个维度里，温度、寿命、外观三项是"带数字"的硬线，介质和载荷决定芯层与界面怎么配。把六个数报齐，路线基本就出来了。
文字版结论：寿命这一维最容易被忽略。五年一换的装饰条，和设计寿命二十几年的外墙型材，用同一套加速老化小时数去要求本身就不合理。先定寿命，再定体系——这是共挤型材选型的第一句话。
三、共挤型材三条材料路线：表层和芯层怎么分工
这个件的材料路线有三种，区别不在"谁更好"，在表层和芯层怎么分工。
| 路线 | 表层 / 芯层怎么分 | 拿到什么 | 付出的代价 |
|---|
| 单层耐候改性PP | 表层芯层同一料，UV 助剂全量加 | 成本低、工艺简单 | 耐候与刚性互相牵制；浅色易褪色；寿命有限 |
| 共挤改性PP + ASA（本篇主线） | 表层 ASA 管耐候外观，芯层 PP 管刚性尺寸成本 | 分工清晰，耐候与刚性可分别优化 | 多一套共挤机头与界面控制 |
| 三层共挤改性PP（PP + 相容层 + ASA） | 中间加相容层 | 界面最稳，可上极性差异大的表层 | 成本最高，工艺最复杂 |
选哪条，取决于这个件最怕什么：怕褪色和脆化→表层必须本征耐候；怕成本→芯层走填充 PP；怕分层→上相容层。三者是分工关系，不是优劣关系。
文字版结论：共挤的本质是"责任分层"。表层专职对抗紫外与保持外观，芯层专职提供刚性、尺寸稳定和成本空间。把两层的事压在一层上，是户外长寿命件最常见的错法。
四、★ 共挤门窗型材选型判据表：五项指标带验证方法
下面这张表是全篇最该收藏的——指标、门限、验证方法、常见失效、通行解法，五列一次给齐。第四列"验证方法"是换料时最容易卡住的地方。
| 指标 | 门限值 | 验证方法 · 标准号 | 常见失效 | 通行解法 |
|---|
| 表层色差 ΔE | ≤3.0（氙灯老化后） | GB/T 16422.2 / ISO 4892-2，时长 1000-2000 h | 褪色、失光 | 表层用 ASA 或高耐候 PP + 稳定剂 |
| 粉化等级 | 无可见粉化（目视 / 灰度） | GB/T 16422.2 老化后评 | 表面起白霜、掉粉 | 表层走本征耐候体系（ASA） |
| 老化后冲击保留率 | ≥90%（抗 UV 强度保持率，A 级旁证 JT/T 1432.1-2022） | JT/T 1432.1-2022（土工格栅口径） | 脆化 | 炭黑 + HALS（深色）/ UV 吸收剂 + HALS（浅色） |
| 共挤界面剥离强度 | 不分层，剥离力达技术协议门限 | EN 513:2018 附录取材（涂层 / 共挤层附着力、剥离强度） | 分层、界面发白 | 同体系相容，必要时加相容层 |
| 温度循环后直线度 | 弯曲 / 扭转在公差内 | 温度循环（−20℃↔60℃，若干循环）后测 | 翘曲、扭转 | 表层芯层线膨胀系数匹配 |
文字版结论：五项是逐级过关的关系。ΔE 和粉化看"外观"，冲击保留率看"力学"，剥离强度看"界面"，直线度看"尺寸"。任何一级不过，先退回那一级改，不要一路冲到整件装配才发现。
五、改性PP共挤型材三类常见失效：根因在表层与芯层配合
改性PP 共挤型材最容易出的三类失效，根因多半不在料本身，在表层和芯层的配合。
失效一：表层粉化、褪色。 根因是单层 PP 耐候不足、助剂耗尽；或者表层用了普通 PP 却只加了紫外吸收剂没加 HALS。
敢否定一个常见做法：有人为了省事，表层就用普通耐候 PP、只上紫外吸收剂。这是错的。紫外吸收剂负责"挡"、HALS 负责"抓"，只加一种，自由基链反应补不齐——户外几年后该粉化还是粉化。表层要本征耐候，要么上 ASA，要么炭黑 + HALS 双体系齐上。
失效二：共挤分层、界面发白。 根因是表层与芯层相容不足，或共挤机头温度不匹配导致界面结合弱。据行业公开资料，共挤料与基料因塑化温度、线膨胀系数、黏度差异，界面会聚集相互作用力，低温和外力下容易破坏。
失效三：型材翘曲、扭转。 根因是表层与芯层线膨胀系数不同，温度循环积聚内应力。PP 芯层约 (4-8)×10⁻⁵/K（GB/T 1036），ASA 表层约 (7-9)×10⁻⁵/°C（行业公开资料），差一档就够在长件上弯出来。
失效四：浅色件褪色快。 根因是浅色不能靠炭黑，只能靠 UV 吸收剂 + HALS，而颜料本身可能先于树脂变色。
六、改性PP共挤型材验证顺序：先外观后力学再界面再尺寸
验证顺序决定换料省钱还是烧钱。顺序错了，成本会在最后一步集中爆出来。
| 顺序 | 验什么 | 不过就退回 |
|---|
| ① 外观 | 色差 ΔE、粉化等级（氙灯老化后） | 退回表层配方 |
| ② 力学保留 | 老化后冲击强度保留率 | 退回耐候体系 |
| ③ 界面 | 共挤剥离强度（参照 EN 513 附录取材） | 退回相容 / 共挤工艺 |
| ④ 尺寸 | 温度循环后直线度 | 退回材料匹配 / 定型 |
| ⑤ 整件装配 | 间隙、装配力、启闭 | 最后才上机 |
每一步都有明确的"不过就退回上一级"判据。最常见的错是跳过 ① ② 直接进 ③——用试模件去判断材料耐候，试模条件往往是临时的，测出来的数没有代表性。
文字版结论：验证顺序是 外观 → 力学 → 界面 → 尺寸 → 装配。外观和力学不过，根本轮不到谈界面和尺寸，因为那说明表层耐候方向就错了。
七、反向诚实：三种情况门窗型材不该用改性PP硬撑
先把不该用的情形讲清楚，比讲怎么选更有价值——三种情况这个件不该用改性PP 硬撑。
情况一：要求 A 级高光镜面、且长期保持。 改性PP 共挤表层做高光可以，但镜面级长期耐候保持不是它的强项，该看铝合金型材或 PVC 高光型材。
情况二：要求户外 20 年以上且保持鲜艳深色。 20 年以上的户外鲜艳深色，靠 ASA 共挤表层也难以稳定承诺，通常要走铝合金或经长期验证的专用建筑型材体系，门限写入技术协议。
情况三：要求承担结构荷载（如高层整窗承重构件）。 改性PP 的蠕变是结构性的，靠改性只能缓解。承力构件走铝合金型材或玻纤增强结构型材，材料分工比硬撑更稳。
规律一致：只要出现"两个方向相反的要求同时要"，就说明这个件不该用 PP 硬撑。 硬接下来的单子，最后都要用返工和索赔还回去。
八、换料风险清单：共挤机头与界面是重点
决定试改性PP 共挤之前，这张表先过一遍。客户真正的顾虑往往不是性能，是"我现在的模具和工艺要不要改"。
| 要动的项 | 需要确认什么 | 不做会怎样 |
|---|
| 模具收缩率 | 芯层 PP 收缩率与原方案差，长件上敏感 | 尺寸超差，装配对不上 |
| 共挤机头温度匹配 | 表层与芯层熔体温度窗口是否兼容 | 界面结合弱、分层 |
| 表层厚度 | 共挤表层常见 0.2-0.3 mm 这一档（行业媒体），按技术协议定 | 太薄耐候不足，太厚成本高 |
| 冷却定型 | 双层冷却速率是否一致 | 翘曲、内应力 |
| 界面相容 | 表层与芯层是否同体系、要不要相容层 | 剥离、发白 |
| 色差 | 浅色件必须先确认色板再上机 | 批次色差争议 |
| 验证顺序 | 外观 → 力学 → 界面 → 尺寸 → 装配 | 风险压到最后一步爆发 |
文字版结论：换料要动的是模具、机头、界面三块，其中最该先谈的是验证顺序。跳过小样直接试模，等于把成本提前花出去；跳过界面直接批量，一次分层就是整批损失。
九、一页纸汇报：共挤门窗型材选型对照表
下面这张一页纸汇报表，让技术员能把结论直接往上报，不必重新组织语言。
| 场景 | 推荐路线 | 关键指标 | 验证标准 | 需先确认条件 |
|---|
| 深色户外门窗型材 | 共挤改性PP + ASA（芯层炭黑 + HALS） | ΔE≤3.0；冲击保留≥90% | GB/T 16422.2；JT/T 1432.1-2022 | 暴露等级、设计寿命 |
| 浅色彩色型材 | 共挤改性PP + ASA（UV 吸收剂 + HALS） | 同上；颜料不先变色 | 同上 | 颜色、色差门限 |
| 高刚性低成本内衬 | 芯层高填充 / 抗冲共聚 PP | 刚性、收缩率 | GB/T 1036、GB/T 17037.4 | 收缩率、装配间隙 |
| 严苛界面要求 | 三层共挤 + 相容层 | 剥离强度达协议 | EN 513:2018 附录取材 | 相容层牌号、机头 |
文字版结论：这张表的作用是让技术员能把结论直接往上报。判断标准只有一条——客户拿这张表，能不能在一次会议里把材料方向定下来。
十、门窗型材最容易出的问题，往往不在料本身
共挤门窗型材行业里有一类失效非常典型：料没有问题，件出了问题。公开技术资料里讲得直接——户外 PP 件会沿粉化、褪色、脆化三条路径衰退，单加紫外吸收剂补不齐，必须紫外吸收剂与 HALS 复配，或表层换本征耐候的 ASA（据行业公开资料，ASA 以丙烯酸酯橡胶相提供本征耐候，不依赖会耗尽的牺牲型稳定剂包）。
公开判据也给了。氙灯老化按 GB/T 16422.2（对应 ISO 4892-2），色差 ΔE≤3.0 作为可接受门槛（参照 GB/T 24149.1-2009 对汽车外饰件的口径），典型评价时长 1000-2000 h；户外件另有附加口径——UV + 热老化 500-1000 h 后性能不下降（据公开技术资料）；深色件还能借炭黑这个量化抓手，JT/T 1432.1-2022 口径炭黑含量 ≥2.0%、抗 UV 强度保持率 ≥90%。
行业通行的做法是把耐候责任交给表层：表层 ASA 或高耐候 PP 管 UV 与外观，芯层 PP 管刚性、尺寸与成本；表层与芯层同为聚烯烃体系更好粘，极性差异大又不加相容层，就会分层、剥离、界面发白。线膨胀系数也要匹配——PP 芯层 (4-8)×10⁻⁵/K，ASA 表层 (7-9)×10⁻⁵/°C，差一档温度循环就弯。
宁波市科隆新材料有限公司在这个件上常供的是改性PP 共挤方向里的耐候与填充方案：按暴露等级给到表层耐候体系（ASA 共挤或炭黑 + HALS / UV 吸收剂 + HALS）与芯层刚性填充方案，配方按件的工况调，可配合打样共研，小批量多牌号的共挤试料需求也能接。
| 工况 | 关键判据 | 科隆常规供应 |
|---|
| 共挤门窗型材表层 | 耐候 + 界面（EN 513 附录取材） | 耐候改性PP + ASA 共挤方向，按暴露等级调 |
| 芯层刚性 / 尺寸 | 收缩率、刚性（GB/T 1036） | 高填充 / 抗冲共聚 PP 芯层 |
| 浅色耐候 | UV 吸收剂 + HALS，颜料不先变色 | 浅色耐候体系方向 |
想提醒一句：件出问题，最常见的错法是先换料。粉化、分层、翘曲——每一条的原因都不止一个。先定位，再换料；顺序反了，往往换了几轮还在原地。
常见问答
问：门窗型材共挤，表层一定要用 ASA 吗？
答：不一定。深色 / 黑色件可以用炭黑 + HALS 的耐候 PP 做表层；浅色彩色件因为不能靠炭黑，更常见走 ASA 或 UV 吸收剂 + HALS 路线。分工才是关键，表层管耐候与外观，芯层管刚性、尺寸与成本。
问：共挤分层是怎么来的，能提前发现吗？
答：多数来自表层与芯层相容不足，或共挤机头温度不匹配导致界面结合弱。可以参照 EN 513:2018 附录取材做界面剥离 / 附着力评价，试模前先打小样看界面，比上机后整批报废省得多。
问：浅色型材为什么褪色比深色快？
答：深色可以靠炭黑这个量化耐候抓手（JT/T 1432.1-2022 口径炭黑 ≥2.0%、抗 UV 强度保持率 ≥90%），浅色没有这层保护，只能靠 UV 吸收剂 + HALS，且颜料本身可能先变色。所以浅色件验证方案不能照抄深色件。
问：温度循环后型材弯了，是料的问题吗？
答：不一定。表层与芯层线膨胀系数不同（PP 约 4-8×10⁻⁵/K，ASA 约 7-9×10⁻⁵/°C），温度循环会积聚内应力导致弯曲扭转。先测温度循环后的直线度，再判断是材料匹配问题还是模具 / 定型问题。
关于我们
样品寄出去之后，我们一般还会多问一句："打算怎么试？"
因为试法不对，好料也能试出坏结果。改性PP 共挤料尤其如此——表层厚度、机头温度匹配、界面相容性，任何一项没到位，结论都会跑偏。
宁波市科隆新材料有限公司，自产改性聚丙烯（PP）造粒，覆盖均聚 / 无规共聚 / 抗冲共聚三档基材，以及填充、玻纤增强、增韧、阻燃、低气味低 VOC、耐候、免喷涂耐划伤等改性方向；按件的工况调配方、可配合打样共研、能接小批量多牌号需求。
Door and window profiles use co-extruded weather-resistant PP ASA. The key is not 'which material is better,' but rather the UV resistance and appearance of the surface layer, and the rigidity, dimensions, and cost of the core layer. This article explains the co-extruded double-layer structure, three degradation paths, five criteria, validation order, and the risks of material substitution, and also specifies the three situations in which this part should not be supported with modified PP.
- Reference: Trade Edition 'How to Choose Weather-Resistant PP' (PP-M7, from a formulation perspective, this article deliberately does not repeat its main content)
There is a layer of white powder on the surface of the door and window profiles, which comes off when you wipe it with your hand, and the color also becomes lighter—this is the most common type of failure people ask about with modified PP co-extrusion materials.
Don't rush to change the material yet. Take a look to see if the chalking is concentrated on the south-facing side or evenly distributed overall, then ask one more question: Was this part originally designed as co-extruded double layer, or single-layer weather-resistant PP 'forcefully toughened'?—For the same batch of material, the conclusions are completely different in the two cases.
1. Outdoor door and window profiles, single-layer weather-resistant PP cannot withstand three degradation pathways
Outdoor door and window profiles cannot rely solely on a single layer of weather-resistant PP to withstand UV — pure PP will degrade along three paths simultaneously: chalking, fading, and embrittlement. Adding additives can only delay it, not change the direction.
Pure PP profiles used outdoors cannot rely on a single layer of material for weather resistance. It will deteriorate along three paths simultaneously: chalking (surface degradation caused by a white frost), fading (increase in color difference ΔE), and embrittlement (decline in impact strength). Adding UV additives can only delay it, not change the direction.
The conclusion should be stated clearly first: outdoor long-life components achieve weather resistance through 'design', not by 'adding an additive'. The co-extrusion method assigns the entire responsibility for weather resistance to the outer layer.
An expert detail: The tertiary C-H bonds on the PP main chain have lower bond energy, making PP more susceptible to UV-induced hydrogen abstraction and chain scission than PE. Therefore, in the same outdoor environment, PP ages faster than PE structurally—this is not a formulation-level issue but a difference in the base material itself. Using intrinsically weather-resistant ASA for the surface layer is equivalent to compensating for this initial difference in the surface layer.
2. Six-dimensional disassembly of door and window profiles under working conditions: Four dimensions must be given with numbers
For the co-extrusion of door and window profiles, first separate the six dimensions; at least four dimensions need to be specified with concrete numbers before the directions can be determined.
| Dimension | The real operating condition of this part | Requirements for the materials |
|---|
| Temperature | Outdoors −20°C to 60°C; higher in areas facing south with no shade and exposed to sunlight; temperature cycling −20°C ↔ 60°C | Not brittle in low temperatures, not soft when hot, does not deform after repeated cycles |
| Load | Wind pressure, opening and closing fatigue, assembly constraints; long-term wind load and self-weight | Sufficient rigidity, low creep |
| Medium | Rain, ultraviolet, salt spray, window cleaner | Weather-resistant Chemical-resistant |
| Lifespan | The typical design life is 10-25 years, classified according to exposure levels | Performance does not deteriorate after long-term aging |
| Appearance | Color difference ΔE≤3.0 (after xenon lamp aging), surface without chalking | Color and gloss stability |
| Compliance | Evaluation can refer to the aging and dimensional standards for building profiles (such as EN 513:2018, GB/T 8814, etc.) | Set according to region of use |
Among the six dimensions, temperature, lifespan, and appearance are 'hard lines with numbers,' while the medium and load determine how the core layer and interface are matched. Once the six numbers are reported, the route is basically set.
Text-based conclusion: Lifespan is the dimension most easily overlooked. Using the same set of accelerated aging hours to assess decorative strips that are replaced every five years and exterior wall profiles designed to last over twenty years is inherently unreasonable. First, determine the lifespan, then determine the system—this is the first sentence in selecting co-extruded profiles.
3. Three material routes for co-extruded profiles: how to divide the work between the surface layer and the core layer
There are three material routes for this part, and the difference is not about 'which is better,' but about how the surface layer and core layer are divided in their roles.
| Route | How to distinguish between the surface layer and the core layer | Get what | The price paid |
|---|
| Single-layer weather-resistant modified PP | The surface layer and core layer use the same material, with the full amount of UV additives added. | Low cost, simple process | Weather resistance and rigidity restrict each other; light colors fade easily; limited lifespan |
| Co-extruded Modified PP ASA (Main Topic of This Article) | Surface layer ASA pipe has weather-resistant appearance, core layer PP pipe has rigidity, dimensions, and cost | Clear division of labor, weather resistance and rigidity can be optimized separately | An additional co-extrusion die and interface control |
| Three-layer co-extruded modified PP (PP compatible layer ASA) | Add a compatible layer in the middle | The interface is the most stable and can be applied to surface layers with large polarity differences | Highest cost, most complex process |
Which one to choose depends on what this part fears most: afraid of fading and embrittlement → the surface layer must be inherently weather-resistant; afraid of cost → the core layer uses filled PP; afraid of delamination → add a compatibilizer layer. The three have a division of labor, not a hierarchy of advantages and disadvantages.
Text version conclusion: The essence of co-extrusion is 'layered responsibility.' The outer layer is dedicated to resisting UV and maintaining appearance, while the core layer is dedicated to providing rigidity, dimensional stability, and cost margin. Putting the responsibilities of both layers onto one is the most common mistake for long-lasting outdoor parts.
Section 4, ★ Co-extruded Door and Window Profile Selection Criteria Table: Five Indicators with Verification Methods
The table below is the one you should most definitely keep from the entire article—five columns listed at once: indicators, thresholds, validation methods, common failures, and standard solutions. The fourth column, 'validation methods,' is the place where you are most likely to get stuck when changing materials.
| Indicator | Threshold value | Verification Method · Standard Number | Common Failures | Common solution |
|---|
| Surface Color Difference ΔE | ≤3.0 (after xenon lamp aging) | GB/T 16422.2 / ISO 4892-2, duration 1000-2000 h | Fading, loss of shine | Surface layer uses ASA or high weather-resistant PP stabilizer |
| Powdering grade | No visible powdering (visual / grayscale) | GB/T 16422.2 Evaluation after aging | White frost on the surface, powder falling off | Surface layer with intrinsic weather-resistant system (ASA) |
| Impact retention after aging | ≥90% (UV resistance retention rate, Class A, JT/T 1432.1-2022) | JT/T 1432.1-2022 (Soil Geogrid Aperture) | Brittle | Carbon black HALS (dark) / UV absorber HALS (light) |
| Co-extrusion interface peel strength | No stratification, peeling force reaches the technical specification threshold | EN 513:2018 Appendix Sampling (Coating / Coextrusion Layer Adhesion, Peel Strength) | Layering, interface whitening | Compatible with the same system, add a compatibility layer if necessary |
| Linearity after temperature cycling | Bending / twisting within tolerance | Measured after temperature cycling (−20℃↔60℃, several cycles) | Warping, twisting | Matching of linear expansion coefficients of surface layer and core layer |
Text Version Conclusion: The five items have a step-by-step pass relationship. ΔE and chalking are judged by 'appearance,' impact retention by 'mechanics,' peel strength by 'interface,' and straightness by 'dimensions.' If any level fails, return to that level for correction first, rather than pushing all the way to the final assembly before discovering it.
5. Three common failures of modified PP co-extruded profiles: the root cause lies in the coordination between the surface layer and the core layer
The three most common types of failure of modified PP co-extruded profiles are mostly not due to the material itself, but in the coordination between the surface layer and the core layer.
Failure 1: Surface chalking and fading. The root cause is insufficient weather resistance of single-layer PP and depletion of additives; or the surface layer uses ordinary PP but only includes a UV absorber without adding HALS.
Can we deny a common practice: some people, for the sake of convenience, only use ordinary weather-resistant PP for the surface layer and just add UV absorbers. This is wrong. UV absorbers are responsible for 'blocking,' while HALS are responsible for 'capturing'; adding only one of them cannot fully compensate for the free radical chain reaction—after a few years outdoors, it will still chalk. The surface layer needs intrinsic weather resistance, either using ASA, or using a dual system of carbon black and HALS.
Failure 2: Co-extrusion delamination and whitening at the interface. The root cause is insufficient compatibility between the surface layer and the core layer, or weak interface bonding caused by mismatched temperatures at the co-extrusion die. According to industry public information, due to differences in plasticizing temperature, linear expansion coefficient, and viscosity between the co-extrusion material and the base material, forces tend to accumulate at the interface, which can be easily damaged under low temperatures and external forces.
Failure 3: Profile warping and twisting. The root cause is the different linear expansion coefficients between the surface layer and the core layer, which accumulates internal stress through temperature cycling. The PP core layer is about (4-8)×10⁻⁵/K (GB/T 1036), and the ASA surface layer is about (7-9)×10⁻⁵/°C (public industry data); even a small difference can cause long parts to bend.
Failure Four: Light-colored parts fade quickly. The root cause is that light colors cannot rely on carbon black and can only rely on UV absorbers and HALS, while the pigment itself may discolor before the resin.
6. Verification sequence for modified PP co-extruded profiles: first appearance, then mechanical properties, then interface, then dimensions
The verification sequence determines whether changing materials saves money or wastes money. If the sequence is wrong, the costs will explode all at once in the final step.
| Order | Test what | But just return |
|---|
| ① Appearance | Color difference ΔE, chalking grade (after xenon lamp aging) | Return to superficial formula |
| ② Mechanical retention | Retention rate of impact strength after aging | Return the weather-resistant system |
| ③ Interface | Co-extrusion peel strength (refer to material from Annex of EN 513) | Return to compatible / co-extrusion process |
| ④ Size | Linearity after temperature cycling | Return Material Matching / Setting |
| ⑤ Complete assembly | Clearance, assembly force, opening and closing | Got on the computer last |
Every step has clear 'just go back to the previous level' criteria. The most common mistake is skipping steps ① and ② and going straight to ③ — using trial molds to judge material weather resistance, the trial mold conditions are often temporary, and the measured numbers are not representative.
Text version conclusion: The verification order is appearance → mechanics → interface → dimensions → assembly. If appearance and mechanics fail, there is no question of discussing the interface and dimensions, because that indicates the surface weathering direction is fundamentally wrong.
7. Reverse Honesty: Three Situations Where Window and Door Profiles Should Not Use Modified PP Rigid Support
It's more valuable to first clarify the situations where it shouldn't be used rather than how to choose—there are three situations where this part shouldn't be made from modified PP no matter what.
Situation one: Requires A-grade high-gloss mirror finish and long-term maintenance. Modified PP co-extruded surface can achieve high gloss, but long-term mirror-level weather resistance is not its strength. Aluminum alloy profiles or PVC high-gloss profiles should be considered.
Scenario 2: Requires outdoor use for more than 20 years while maintaining bright dark colors. For outdoor bright dark colors lasting more than 20 years, it is difficult to reliably guarantee stability even with an ASA co-extruded surface layer. Usually, aluminum alloy or long-validated specialized architectural profile systems are needed, and the threshold should be written into the technical agreement.
Scenario 3: Required to bear structural loads (such as load-bearing components of full-height windows in high-rise buildings). The creep of modified PP is structural and can only be alleviated through modification. Load-bearing components should use aluminum alloy profiles or glass fiber reinforced structural profiles, as material specialization is more stable than rigid support.
Consistent pattern: Whenever there is a 'requirement for two opposite directions at the same time', it indicates that this piece should not be forcibly made with PP. Forcing the next orders will eventually lead to rework and claims for return.
8. Material Change Risk List: The co-extruder head and interface are the key points
Before deciding to trial modified PP co-extrusion, go through this table first. The client's real concern is often not performance, but 'do I need to change my current molds and processes?'
| Items to move | What needs to be confirmed | What will happen if I don't do it? |
|---|
| Mold shrinkage rate | The shrinkage rate of the core layer PP is different from the original plan and is sensitive on long parts. | The dimensions are out of tolerance, and the assembly does not fit. |
| Coextrusion die temperature matching | Are the melt temperature windows of the skin layer and core layer compatible? | Weak interface integration, layered |
| Surface thickness | The common co-extruded surface thickness is 0.2-0.3 mm (industry media), as specified by the technical agreement | Too thin, lacks weather resistance; too thick, high cost |
| Cooling and shaping | Is the cooling rate of the double layer consistent? | Warping, internal stress |
| Interface Compatibility | Whether the surface layer and core layer are of the same system, and whether a compatible layer is needed | Peeling, whitening |
| Color difference | Light-colored parts must confirm the color swatch before being put on the machine | Batch color difference dispute |
| Verification order | Appearance → Mechanics → Interface → Dimensions → Assembly | The risk erupts at the very last step |
Text version conclusion: Changing materials involves three parts: mold, nozzle, and interface, among which the verification order should be discussed first. Skipping small samples and testing the mold directly is equivalent to spending the cost in advance; skipping the interface and going straight to batch production can result in the loss of the entire batch in one layer.
9. One-page report: Comparison table for selecting extruded profiles for doors and windows
The following one-page report allows technicians to directly submit conclusions upward without having to reorganize their language.
| Scene | Recommended Route | Key indicators | Verification Standard | Conditions need to be confirmed first |
|---|
| Dark-colored outdoor door and window profiles | Co-extruded modified PP ASA (core layer carbon black HALS) | ΔE ≤ 3.0; impact retention ≥ 90% | GB/T 16422.2; JT/T 1432.1-2022 | Exposure level, design life |
| Light-colored profiles | Co-extruded modified PP ASA (UV absorber HALS) | Same as above; the pigment does not change color first | Same as above | Color, color difference threshold |
| High-rigidity low-cost lining | Core layer high-fill / impact-resistant copolymer PP | Rigidity, shrinkage rate | GB/T 1036, GB/T 17037.4 | Shrinkage rate, assembly clearance |
| Strict interface requirements | Three-layer co-extrusion compatible layer | Peel strength meets the agreement | EN 513:2018 Appendix Material Selection | Compatible layer grade, print head |
Text version conclusion: The purpose of this table is to allow technicians to report conclusions directly. There is only one criterion for judgment — whether the customer can use this table to determine the direction of the materials in a single meeting.
10. The problems that occur most easily with door and window profiles often do not lie in the material itself.
In the co-extruded door and window profile industry, there is a very typical type of failure: the material is fine, but the part fails. Public technical information explains it directly — outdoor PP parts degrade along three paths: chalking, fading, and brittleness. Using only UV absorbers is not enough; UV absorbers must be combined with HALS, or the surface layer must be replaced with intrinsically weather-resistant ASA (according to industry public information, ASA provides intrinsic weather resistance through its acrylate rubber phase, without relying on expendable stabilizer packages that will be depleted).
The public criteria are also provided. Xenon lamp aging follows GB/T 16422.2 (corresponding to ISO 4892-2), with a color difference ΔE≤3.0 as an acceptable threshold (referring to the criterion for automotive exterior parts in GB/T 24149.1-2009), with a typical evaluation duration of 1000-2000 hours; for outdoor parts, there are additional criteria—performance should not decrease after 500-1000 hours of UV and heat aging (according to publicly available technical information); for dark-colored parts, carbon black can be used as a quantifiable means, with JT/T 1432.1-2022 specifying a carbon black content ≥2.0% and a UV resistance retention rate ≥90%.
The common industry practice is to assign weather resistance to the outer layer: the outer layer ASA or high-weather-resistance PP handles UV and appearance, while the PP core handles rigidity, dimensions, and cost; having both the outer and core layers in the polyolefin system improves adhesion. If the polarity difference is large and no compatibilizer layer is added, delamination, peeling, and interface whitening will occur. The coefficients of linear expansion also need to match — PP core (4-8)×10⁻⁵/K, ASA outer layer (7-9)×10⁻⁵/°C; even a one-grade difference in temperature cycling can cause bending.
Ningbo Kelong New Materials Co., Ltd. commonly supplies weather-resistant and filled solutions for modified PP co-extrusion in this part: according to the exposure level, the surface layer is provided with a weather-resistant system (ASA co-extrusion or carbon black HALS/UV absorber HALS) and the core layer with a rigidity filler scheme. The formulation is adjusted according to the working conditions of the part, and it can cooperate in joint development for sample trials. Small-batch, multi-grade co-extrusion trial material requests can also be accommodated.
| Operating condition | Key criterion | Cologne regular supply |
|---|
| Co-extruded door and window profile surface | Weathering Interface (Material taken from EN 513 Appendix) | Weather-resistant modified PP ASA co-extrusion orientation, adjusted according to exposure level |
| Core layer rigidity / Dimensions | Shrinkage rate, rigidity (GB/T 1036) | High-filled / Impact-resistant Copolymer PP Core Layer |
| Light-colored weather-resistant | UV absorbers HALS, pigments do not discolor first | Light-colored weather-resistant system direction |
Just a reminder: when something goes wrong, the most common mistake is to change the material first. Powdering, delamination, warping — each of these issues has more than one cause. Identify the cause first, then change the material; if the order is reversed, you can go through several rounds of material changes and still be in the same place.
Frequently Asked Questions
Question: For co-extruded door and window profiles, does the surface layer have to use ASA?
Answer: Not necessarily. Dark/black parts can use carbon black HALS weather-resistant PP for the outer layer; for light-colored parts, because carbon black cannot be used, it is more common to use ASA or UV absorber HALS. Division of labor is the key: the outer layer handles weather resistance and appearance, while the core layer handles rigidity, dimensions, and cost.
Question: How does co-extrusion delamination occur, and can it be detected in advance?
Answer: Most of the issues come from insufficient compatibility between the outer layer and the core layer, or weak interface bonding caused by mismatched temperatures at the co-extrusion head. You can refer to the material selection in Appendix of EN 513:2018 to perform interface peel/adhesion evaluation. It is better to make a small sample and check the interface before mold trials, which can save a lot compared to scrapping the entire batch after production.
Question: Why do light-colored profiles fade faster than dark-colored ones?
Answer: Dark colors can rely on carbon black as a quantifiable handle for weather resistance (JT/T 1432.1-2022 caliber carbon black ≥2.0%, UV resistance retention ≥90%), whereas light colors do not have this layer of protection and can only rely on UV absorbers and HALS, and the pigment itself may discolor first. Therefore, the verification scheme for light-colored parts cannot simply copy that of dark-colored parts.
Question: After temperature cycling, the profile bent. Is it a material problem?
Answer: Not necessarily. The linear expansion coefficients of the surface layer and the core layer are different (PP about 4-8×10⁻⁵/K, ASA about 7-9×10⁻⁵/°C), and temperature cycling can accumulate internal stress, causing bending and twisting. First, measure the straightness after temperature cycling, and then determine whether it is a material compatibility issue or a mold/setting issue.
About Us
After sending out the sample, we usually ask one more question: 'How do you plan to test it?'
Because the testing method is incorrect, even good material can yield bad results. This is especially true for modified PP co-extrusion materials—any factor such as surface layer thickness, die temperature matching, or interface compatibility, if not properly addressed, can lead to biased conclusions.
Ningbo Kolon New Materials Co., Ltd. produces modified polypropylene (PP) granules, covering three types of base materials: homopolymer, random copolymer, and impact copolymer, as well as various modification directions such as filled, glass fiber reinforced, toughened, flame retardant, low odor and low VOC, weather-resistant, and scratch-resistant without painting; formulation can be adjusted according to specific working conditions, supporting sample testing and co-development, and able to meet small-batch, multiple-grade requirements.
