汽车空调风道用什么改性PP？答案不在"哪种料更好"，而在柔韧性与低气味怎么平衡。这篇讲清暖风侧持续温热、冷凝水、装配卡扣反复受力、乘员舱 VDA 散发四维工况，给出判据表、验证顺序与换料清单，并说清风道为什么通常不该上玻纤。
"你们这个料，装车的时候卡扣怎么一掰就裂？"
"还有，夏天暴晒完一开车门，那股味儿是不是料的问题？"
这是风道、暖风管这类件最常被人一起问的两个问题。一个问"韧不韧"，一个问"臭不臭"。有意思的是，这两件事在改性PP 上不是各管各的——它们共用同一条基材，又互相牵制。增韧加多了，气味往往更难压；为了低气味把助剂体系收得太紧，柔韧性又可能掉下来。
所以这篇的主线不是"风道用什么料"，而是柔韧性与低气味怎么平衡。先讲工况，再讲路线，最后把验证顺序和换料清单摆清楚。
一、工况六维拆解：暖风侧温热、卡扣反复受力、乘员舱气味门
风道、暖风管挂在仪表台里面，一端接空调箱，一端接出风口。它的工况可以拆成六个维度，把六个数报齐，材料方向基本就定了。
| 维度 | 风道 / 暖风管的实际工况 | 对材料的要求 |
|---|
| 温度 | 暖风侧接触暖风，常见 60–90℃ 持续温热；短时峰值可接近增韧 PP 短时承受的 140℃ 热负荷；空调侧随环境温度到低温 | 短时耐热 + 长期温热不变形 |
| 载荷 | 不是大静载，是装配卡扣反复插拔 / 受力，按整车生命周期循环可达数千次；道路随机振动持续作用 | 卡扣柔韧、抗疲劳，不脆崩 |
| 介质 | 空调侧结露产生冷凝水（相对湿度接近饱和）+ 灰尘；暖风侧干燥温热 | 耐湿热、不积水发味 |
| 寿命 | 整车生命周期，常按 10 年 / 15 万公里级设计 | 长期老化后柔韧不塌、气味不升 |
| 外观 | 内壁常可见，出风口件要看得见内壁；浮纤、缩痕、色差直接暴露 | 表面干净、色差可控 |
| 合规 | 件在乘员舱内，气流直吹人；行业通行参照德系 VDA 口径：气味 ≤3 级（VDA 270）、甲醛 ≤10 mg/kg（VDA 275）、冷凝组分 ≤2 mg（VDA 278 / DIN 75201）、总碳 TVOC ≤50 μgC/g（VDA 277，德系常压到 ≤30） | 四项散发全过门 |
六个维度里，合规这一维是"硬门"——它离乘员鼻子最近，吹出来的风贴着内壁走，料里任何挥发物都被人直接吸进去。而温度这一维决定基材能不能扛住暖风；载荷这一维决定卡扣会不会崩。三者一起看，才谈得上"柔韧与低气味平衡"。
一个内行细节：VDA 270 的气味等级是"人鼻嗅辨"的主观分级（1–6 级），能报出标准号与测试温度的供应商，信任度完全不一样。很多采购只会问"气味达标吗"，不会问"按哪个标准、几级、几个温度舱"——这一句就能筛掉一半不专业的料。
二、三条材料路线怎么分：增韧PP / 共聚PP+增韧 / 弹性体体系
改性PP 的基体是聚丙烯，本身偏脆、韧性有限，要做风道必须往"柔"的方向走。行业内大致三条并列路线，不构成"谁更好"，只在分工边界上不同。
| 路线 | 拿到什么 | 代价 / 边界 |
|---|
| 增韧 PP（抗冲共聚 PP + EPDM/POE 增韧） | 卡扣柔韧、低温抗崩、低气味靠低挥发助剂体系，主体不上玻纤 | 刚性偏低，不适合当承力结构 |
| 共聚 PP 基材 + 增韧（抗冲共聚打底，增韧剂加量按需调） | 先定基材档位再调增韧，配方起点更灵活；低气味体系同源 | 与上一路线本质同族，区别在配方起点与自由度 |
| 弹性体体系（TPO / POE 高比例共混） | 柔韧与阻尼更好，对降噪有帮助，大变形段更耐疲劳 | 刚性更低、尺寸稳定性稍弱，不适合要刚度的段 |
三条路线没有优劣。分法很朴素：
- 风道、暖风管主体要"柔 + 不臭 + 能降噪" → 走增韧 PP 或共聚 PP + 增韧；
- 对静音极敏感、或段要承受大变形的部位 → 看弹性体体系；
- 需要刚度、耐蠕变、尺寸稳的（导风罩、风扇叶）→ 那是另一类，走玻纤增强 PP，不在本篇路线内。
真正难的是"柔"和"不臭"怎么同时拿到手：增韧相（乙丙橡胶、POE）本身是低分子量的软相，热稳定性比均聚基体差，一旦注塑温度过高就容易局部分解产生异味；而低气味体系又要从源头压低所有助剂的挥发。两条要求落在同一颗粒子上，配方要的是排序，不是堆料。
三、★ 选型判据表：五项指标，每项带验证方法
下面这张表是全篇最该收藏的部分。注意第三列"验证方法·标准号"——风道选材最常卡住的不是"看哪个指标"，而是"拿什么测、测到多少算过"。物性值注"典型值，以牌号 TDS 为准"；VDA 类为行业通行参照口径，不是强制国标，订货要写进技术协议。
| 指标 | 门限值 | 验证方法 · 标准号 | 常见失效 | 通行解法 |
|---|
| 气味 | ≤3 级 | VDA 270（人鼻嗅辨，常做 23℃/40℃/80℃ 多温度舱） | 暴晒后车内异味重、投诉 | 低气味体系 + 控脱模剂 / 料温 |
| 甲醛 | ≤10 mg/kg | VDA 275 | 散发门限不过，整车验收卡 | 低挥发助剂 + 充分干燥 |
| 冷凝组分 | ≤2 mg | VDA 278 / DIN 75201 | 冷凝液异味、起雾 | 低挥发配方源头压 |
| 总碳 TVOC | ≤50 μgC/g（德系常压到 ≤30） | VDA 277 | 挥发物被直吹乘员舱 | 低气味体系整体设计 |
| 卡扣装配柔韧（低温缺口冲击） | 按件取适用温度档留余量，如 −20~−30℃ 取适用值 | GB/T 1043.1（简支梁） | 装配卡扣崩裂 | 抗冲共聚 + 增韧 |
| 短时耐温（暖风侧） | 短时承受 140℃ 热负荷 | 短时热老化 + 耐热测试（如 GB/T 1634 负荷变形温度思路） | 暖风管长期温热软化变形 | 增韧 PP（短时 140℃） |
| MFR 流动性 | 按流程比取中高档（薄壁长流程参考 20–45 g/10min） | GB/T 3682.1（230℃/2.16 kg） | 充填不足、短射、流痕 | 抗冲共聚选中高 MFR |
| 收缩率 / 尺寸 | 收缩率按模具定，大长件对收缩极敏感 | GB/T 17037.4 / ISO 294-4 | 装配间隙对不上 | 滑石粉少量调尺寸（≤10%） |
文字版结论：八项里气味四项（VDA 270/275/277/278）与卡扣柔韧是最该先看的两组——前者是乘员舱硬门，后者是装配硬门；短时耐热 140℃ 决定暖风侧能不能用增韧 PP；MFR 与增韧是反向的，加韧必然损失流动性，所以要一起定；收缩率不是"料自己的事"，它要和客户的模具一起看。把这张表当成体检单，缺一项不判合格，比装车后回头找原因省钱得多。
四、常见失效与根因：四个现象，四条根因
失效一：装配卡扣崩裂。 根因多数不是"料太脆"一句话，而是三点之一——用了均聚 / 无规而非抗冲共聚基材、增韧加量不够、或卡扣根部壁厚减薄过快导致应力集中。先查壁厚设计，再查基材档位，最后查增韧量，顺序反了会白换几轮。
失效二：暴晒后车内异味重。 根因不只是料。一个公开案例值得每个做内饰的人记住：某供应链里出现过"改性 PP 粒子的气味检测合格，但最终塑料件的气味却超标"。产业链跟踪后找到两个原因——注塑时喷了过量的脱模剂引入杂味，以及注塑温度过高导致材料部分分解产生异味。论文结论是：要彻底解决塑料件气味问题，需要汽车厂、零部件企业、原材料商三方共同努力。把气味问题全推给料厂，是这一行最常见的错法。
失效三：暖风管长期温热后软化变形。 根因是误用了耐热不足的普通 PP，或实际工况长期超过增韧 PP 短时承受的 140℃ 热负荷。增韧 PP 扛得住短时峰值，不等于扛得住长期超温——这条要进反向诚实段。
失效四（敢否定最强的一条）：风道上了玻纤以为"更结实"。 素材库把"空调风道 / 导风罩 / 风扇叶"归在同一行，都写 PP-GF20/GF30，但这是把"送风管"和"结构件"混在了一行。风道要的是柔韧 + 降噪，上玻纤会抬高刚性、降低阻尼、还可能引入异响和内壁浮纤，方向完全反了。风道主体不该上玻纤；需要刚度、耐蠕变的是导风罩、风扇叶，那才走玻纤增强路线。 把风扇叶的玻纤料搬来打风道，外观和静音都会翻车。
五、验证顺序：先验什么，后验什么
这一段同行几乎没人写，但它是换料能不能省钱、气味能不能过门的关键。顺序错了，问题会在装车那一刻才爆出来。
`
① 小样物理比对 气味四项（VDA 270/275/277/278）+ 缺口冲击 + MFR + 收缩率
↓ 八项都在门限内，才往下走
② 气味双测 先测粒子气味，再测零件气味（公开案例教训：粒子合格 ≠ 件合格）
↓ 任一项超标，先定位是料还是工艺
③ 工艺窗口验证 料温上限 + 停留时间 + 脱模剂用量 + 干燥条件（打工艺试片）
↓ 这步把"脱模剂 / 料温"两条因果链关进验证清单
④ 短射试模 看充填是否完整、熔接线 / 浮纤、内壁外观
↓ 短射走通，才谈批量
⑤ 装车匹配 卡扣装配力、间隙、实车气味
↓
⑥ 批量试产 + 客户端验证
`
文字版结论：验证顺序是 小样 → 气味双测 → 工艺窗口 → 短射 → 装车匹配 → 批量。气味双测必须在试模之前完成，因为它最能一票否决；工艺窗口（料温 / 脱模剂 / 干燥）要进验证清单，否则装车后异味问题永远查不到根。
六、反向诚实：这三种情况，风道不该用改性PP硬撑
前面讲"怎么做"，这里讲"什么时候别做"。这一段对选型判断的价值最高。
| 出现的情况 | 为什么改性 PP 不合适 | 该往哪走 |
|---|
| 要求长期工作温度 150℃ 以上（暖风长期超温） | 增韧 PP 短时承受 140℃ 热负荷，长期超温其负荷变形温度撑不住，靠填充增强往上抬也有边界 | 换更高耐热的工程塑料或耐热改性体系 |
| 把风道当高刚性承力结构用 | 风道本就不承力；强求刚度要上玻纤，但那会牺牲柔韧与降噪，方向反了 | 结构件与送风管分开设计，承力段走玻纤增强 PP |
| 要求极高表面光泽 + 免喷涂同时 | 高光免喷涂要求表面细腻少填料，与低气味体系的低填充取向可兼容，但与风道"柔韧降噪"的主线冲突，且气味门限照旧 | 表面件走专用免喷涂耐划伤体系，气味门限不可放 |
规律很清楚：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。 遇到这种情况，我们的做法是先把这条讲清楚，再谈有没有折中——硬接下来的单子，最后都要用返工和索赔还回去。
七、换料要动什么：一张先看再动的清单
决定试改性PP 之前，这张表建议先过一遍。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 | 新料收缩率与原方案的差，长件上尤其敏感 | 尺寸超差，卡扣对不上、装配间隙偏 |
| 浇口与排气 | 低气味料中高 MFR 流动差异；风道长流程需排气充分防困气 | 充填不足、困气、内壁缺陷 |
| 料温与模温 | 增韧相热稳定窗口窄（呼应 VW 温度链） | 料温过高分解异味、表面缺陷 |
| 干燥 | 低气味料通常需干燥除水气挥发（直接影响气味） | 不干燥则气味升、银丝 |
| 保压与脱模 | 柔韧料脱模力 / 顶白；脱模剂过量引入杂味（呼应 VW 脱模剂链） | 变形、顶出拉伤、件气味超标 |
| 色差 | 内壁可见，色板必须先确认再上机 | 批次色差争议 |
| 验证顺序 | 小样 → 气味双测 → 工艺窗口 → 短射 → 装车匹配 | 风险全部压到最后一步集中爆发 |
文字版结论：换料要动的是模具、工艺、色差三块，其中最该先谈的是验证顺序和工艺窗口。跳过小样直接试模，等于把成本提前花出去；跳过气味双测和工艺窗口直接批量，一次失败就是整批气味返工。
八、一页纸汇报表（可以直接贴进 PPT）
| 场景 | 推荐路线 | 关键指标 | 验证标准 | 需先确认的条件 |
|---|
| 常规空调风道 | 抗冲共聚 PP + 增韧 + 低气味体系 | 气味四项 VDA 过门；卡扣柔韧留余量；MFR 中高 | VDA 270/275/277/278；GB/T 1043.1；GB/T 3682.1 | 成型方式、拼装 / 焊接方式 |
| 暖风管（接触暖风） | 增韧 PP（短时 140℃） | 短时耐热 140℃；气味四项过门 | 短时热老化 + 耐热测试；VDA 四项 | 暖风实际温度、是否长期 >140℃ |
| 静音 / 大变形段 | 弹性体体系（TPO/POE 高比例） | 阻尼 / 柔韧 / 抗疲劳 | 按件定适用温度档冲击 | 静音要求级别、变形量 |
| 导风罩 / 风扇叶（对比，不在本篇路线） | 玻纤增强 PP GF20-30 | 刚度、耐蠕变、HDT | — | 说明风道与结构件是两套料 |
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，不必重新组织语言。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。 风道与导风罩、风扇叶是两套逻辑，别混着选。
九、这个件上最容易出问题的，往往不是料
风道、暖风管行业最常见的两类失效，一类是装配卡扣崩裂（柔韧不足），一类是暴晒后车内异味（低气味没压住）。公开案例里记录过：改性 PP 粒子的气味检测合格，但最终塑料件气味却超标；产业链跟踪后归因于两条因果链——注塑喷了过量脱模剂引入杂味，以及注塑温度过高导致材料局部分解产生异味；论文结论是要靠材料厂、零部件厂、主机厂三方协同才能彻底解决。这把"归因"讲透了一点：粒子合格是一道门槛，件合格是另一道门槛，而第二道门槛卡在工艺，不在粒子。
行业通行参照的德系 VDA 口径是四项：气味 ≤3 级（VDA 270）、甲醛 ≤10 mg/kg（VDA 275）、冷凝组分 ≤2 mg（VDA 278 / DIN 75201）、总碳 TVOC ≤50 μgC/g（VDA 277）。注意这是主机厂对改性粒子的管控口径，不是国家标准，订货要写进技术协议才管用。
通行的材料路线是抗冲共聚 PP 打底 + 增韧 + 低气味助剂体系，主体通常不上玻纤（外观浮纤、阻尼与降噪都吃亏）；最多少量滑石粉调尺寸。柔韧性和低气味的平衡，靠的是低挥发增韧相、低气味稳定剂与色母，以及把注塑温度上限、停留时间、脱模剂用量、干燥条件一起管住。
宁波市科隆新材料有限公司在这个件上常供的是抗冲共聚聚丙烯 + 增韧 + 低气味体系方向的料，MFR 按成型方式分档，主要用来解决上面说的"卡扣柔韧 + 气味过门"这两件事；对静音 / 大变形段，对应的是弹性体体系方向，按需分开对接。
常见问答
问：风道能不能上玻纤"更结实"？
答：不该。风道要的是柔韧和降噪，玻纤抬高刚性、降低阻尼，还可能带来异响和内壁浮纤；要刚度的是导风罩、风扇叶，走玻纤增强 PP，是另一套料。把结构件的料搬来打风道，外观和静音都会翻车。
问：粒子气味都合格了，件还超标怎么办？
答：先查注塑工艺——脱模剂用量和料温上限是最常见的两条元凶。把这两项连同干燥条件一起写进验证清单，由材料厂给料温上限与脱模建议、零部件厂控工艺、主机厂定门限并验收，三方协同才兜得住。
| 工况 | 关键判据 | 科隆常规供应 |
|---|
| 空调风道 / 暖风管 | 气味四项 VDA 过门；卡扣柔韧；短时耐热 140℃ | 抗冲共聚 PP + 增韧 + 低气味体系方向，MFR 按成型分档 |
| 静音 / 大变形段 | 阻尼 / 柔韧 / 抗疲劳 | 弹性体体系（TPO/POE）方向，按需对接 |
想提醒一句：件出问题，最常见的错法是先换料。卡扣崩了、味儿大了——是基材档位错了、增韧量不够，还是脱模剂喷多了、料温飙了，原因定不准，换几轮粒子还在原地。
十、最后说三句
第一，风道选型的第一句话不是"哪种料好"，是"柔韧和低气味怎么平衡"。 六维工况里合规是硬门、温度是底线、卡扣载荷是装配硬门，三者一起看才定得下基材。
第二，增韧和低气味共用同一条基材，却互相牵制。 增韧相热稳定性差，料温一高就分解异味；低气味体系又要压住所有助剂挥发。配方做的是排序，不是堆料。
第三，验证顺序比验证项更重要。 小样 → 气味双测 → 工艺窗口 → 短射 → 装车匹配；粒子合格不等于件合格，脱模剂与料温两条因果链必须写进验证清单。
下一篇讲另一个汽车功能件——散热器水室与膨胀箱：那件料的逻辑完全不同，是"长期高温 + 冷却液浸泡 + 压力循环"三件事叠在一起。
关于我们
我们交付的，不只是一包料。
还有一句用料的判断、一份对得上的物性表、一个出了问题还能找的人。
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；兼营各大石化厂 PP 树脂、副牌料与大包料。
What type of modified PP is used for automotive air conditioning ducts? The answer is not about "which material is better," but about how to balance flexibility and low odor. This article explains continuous warmth on the heating side, condensation, repeated stress on assembly clips, and four-dimensional conditions of cabin VDA emissions, provides criteria tables, validation sequences, and a material replacement list, and explains why ducts generally should not include glass fiber.
This material of yours, why does the buckle crack as soon as it is snapped when loading?
Also, after being exposed to the sun in summer, when you open the car door, is that smell related to the materials?
These are the two questions most commonly asked together about parts like air ducts and warm air pipes. One asks 'Is it tough?' and the other asks 'Does it stink?' Interestingly, with modified PP, these two issues are not independent—they share the same base material and influence each other. If you add too much toughness, the odor often becomes harder to control; if you tighten the additive system too much to reduce odor, the flexibility may suffer.
So the main focus of this article is not 'what material to use for the air duct,' but how to balance flexibility and low odor. First discuss the working conditions, then the approach, and finally clarify the verification sequence and the material replacement list.
1. Six-dimensional analysis of working conditions: warm air side temperature, repeated stress on clips, passenger compartment odor door
The air ducts and heater pipes are hung inside the instrument panel, one end connected to the air conditioning box and the other end connected to the air outlet. Its operating conditions can be broken down into six dimensions; once the six numbers are matched, the material direction is basically determined.
| Dimension | Actual operating conditions of air duct / warm air pipe | Requirements for the materials |
|---|
| Temperature | The warm air side comes into contact with warm air, commonly maintaining a continuous temperature of 60–90℃; short-term peaks can approach the 140℃ thermal load that toughened PP can withstand briefly; the air conditioning side follows the ambient temperature down to low temperatures. | Short-term heat-resistant, long-term warm without deformation |
| Load | It is not large static load, but the repeated insertion and removal of assembly clips / subjected to force, which can reach thousands of times according to the vehicle's lifecycle; random road vibrations act continuously. | The buckle is flexible and fatigue-resistant, not brittle or prone to breaking. |
| Medium | Condensation occurs on the side of the air conditioner (relative humidity near saturation), along with dust; the warm air side is dry and warm. | Resistant to damp heat and does not accumulate water or become smelly |
| Lifespan | The vehicle's entire lifecycle is commonly designed for 10 years / 150,000 kilometers. | After long-term aging, it remains flexible without collapsing, and the odor does not rise |
| Appearance | The inner wall is often visible, the air outlet parts should allow the inner wall to be seen; floating fibers, shrink marks, and color differences are directly exposed | Clean surface, controllable color difference |
| Compliance | In the passenger cabin, the airflow blows directly on people; industry standards refer to the German VDA specifications: odor ≤ level 3 (VDA 270), formaldehyde ≤ 10 mg/kg (VDA 275), condensate components ≤ 2 mg (VDA 278 / DIN 75201), total carbon TVOC ≤ 50 μgC/g (VDA 277, German standard under normal pressure ≤ 30). | All four types are scattered over the door |
Among the six dimensions, the compliance dimension is a 'hard gate' — it is closest to the passengers' noses, the air it blows flows along the inner wall, and any volatiles in the material are directly inhaled. The temperature dimension determines whether the base material can withstand warm air; the load dimension determines whether the clips will break. Only by looking at all three together can we talk about a 'balance of flexibility and low odor'.
An insider detail: The odor level in VDA 270 is a subjective rating based on the 'human nose' (levels 1–6). Suppliers who can provide the standard number and testing temperature are much more trustworthy. Many buyers will only ask 'Does the odor meet the standard?' and not 'According to which standard, what level, and how many temperature chambers?' — this single question can filter out half of the unprofessional materials.
2. How to differentiate the three material routes: Toughened PP / Copolymer PP Toughened / Elastomer System
The matrix of modified PP is polypropylene, which is inherently brittle and has limited toughness. To make air ducts, it must lean towards being 'soft.' There are roughly three parallel approaches within the industry, which do not constitute 'which is better,' but only differ in the boundaries of their roles.
| Route | Get what | Cost / Boundary |
|---|
| Toughened PP (impact-resistant copolymer PP, EPDM/POE toughened) | The buckle is flexible, resistant to cracking at low temperatures, and has low odor due to a low-volatile additive system, and the main body does not contain glass fiber. | Low rigidity, not suitable as a load-bearing structure |
| Copolymerized PP substrate Toughening (impact-resistant copolymer primer, toughening agent dosage adjusted as needed) | First set the substrate grade and then adjust the toughness, making the formulation starting point more flexible; low-odor system is homologous | Essentially of the same family as the previous route, the difference lies in the starting point of the formula and the degree of freedom |
| Elastomer system (TPO / POE high-ratio blend) | Better flexibility and damping, helpful for noise reduction, and the large deformation section is more fatigue-resistant | Lower rigidity and slightly weaker dimensional stability, not suitable for sections requiring stiffness |
There is no better or worse among the three routes. The classification is very simple:
- The main ducts and heater pipes should be 'flexible, odorless, and noise-reducing' → use impact-modified PP or copolymer PP for toughening;
- For areas extremely sensitive to noise or sections that need to endure large deformations → look at elastomer systems;
- For parts that require stiffness, creep resistance, and dimensional stability (air guide covers, fan blades) → That’s a different category, using glass fiber reinforced PP, which is not covered in this article.
The real difficulty is how to achieve both 'softness' and 'low odor' at the same time: the toughening phase (EPDM, POE) itself is a low molecular weight soft phase, and its thermal stability is worse than that of the homopolymer matrix, so if the injection molding temperature is too high, it can easily decompose locally and produce an unpleasant odor; at the same time, a low-odor system requires suppressing the volatility of all additives from the source. Meeting both requirements in the same particle means that the formulation needs proper sequencing, not just piling on materials.
3. ★ Selection Criteria Table: Five indicators, each with a validation method
The table below is the part of the article most worth saving. Note the third column 'Verification Method · Standard Number' — the most common issue in duct material selection is not 'which indicator to look at,' but 'what to measure with and what value counts as passing.' For physical property values, note 'typical value, based on the TDS of the grade'; VDA types are industry reference standards, not mandatory national standards, and should be included in the technical agreement when ordering.
| Indicator | Threshold value | Verification Method · Standard Number | Common Failures | Common solution |
|---|
| smell | ≤ Grade 3 | VDA 270 (human nose odor evaluation, often done in 23℃/40℃/80℃ multi-temperature chambers) | Strong odor inside the car after sun exposure, complaint | Low-odor system Release agent / Material temperature |
| Formaldehyde | ≤10 mg/kg | VDA 275 | Emission threshold not met, whole vehicle acceptance rejected | Low volatility additives Fully dried |
| Condensate components | ≤2 mg | VDA 278 / DIN 75201 | Condensate odor and fogging | Low-volatility formula source pressing |
| Total Carbon TVOC | ≤50 μgC/g (German standard atmospheric pressure up to ≤30) | VDA 277 | Volatile substances are directly blown into the cabin | Low-odor system overall design |
| Snap-fit assembly flexibility (low-temperature notch impact) | Take the applicable temperature range for each item and leave a margin, for example, take the applicable value for −20~−30℃ | GB/T 1043.1 (Simply Supported Beam) | Assembly clip breakage | Impact Copolymerization Toughening |
| Short-term temperature resistance (warm air side) | Temporarily withstand a heat load of 140℃ | Short-term heat aging Heat resistance test (such as the approach for GB/T 1634 heat distortion temperature) | The warm air duct has been softened and deformed due to long-term heat exposure | Toughened PP (short-term 140℃) |
| MFR Liquidity | According to the process, compare and select mid-to-high grade (thin-wall long process reference 20–45 g/10min) | GB/T 3682.1 (230℃/2.16 kg) | Underfilling, short shot, flow marks | Impact-resistant copolymer selected with medium-high MFR |
| Shrinkage / Dimensions | The shrinkage rate is determined by the mold, and long and large parts are extremely sensitive to shrinkage. | GB/T 17037.4 / ISO 294-4 | The assembly clearance does not match | Talc powder in small amounts for size adjustment (≤10%) |
Text version conclusion: Among the eight items, the four related to odor (VDA 270/275/277/278) and the flexibility of the clips are the two groups that should be checked first—the former concerns passenger cabin hard doors, the latter concerns assembled hard doors; short-term heat resistance at 140°C determines whether reinforced PP can be used on the heater side; MFR and reinforcement are inverse, adding reinforcement will inevitably reduce flowability, so they need to be decided together; shrinkage rate is not just a 'material issue,' it needs to be considered together with the customer's mold. Treat this table like a health check list—if one item is missing, do not deem it qualified. This saves much more money than trying to find the problem after vehicle assembly.
4. Common Failures and Root Causes: Four Phenomena, Four Root Causes
Failure 1: Assembly clip breakage. The root cause is often not simply 'the material is too brittle,' but one of three factors: using homopolymer/random copolymer instead of impact-resistant copolymer material, insufficient toughening, or rapid reduction of wall thickness at the base of the clip causing stress concentration. First check the wall thickness design, then the material grade, and finally the toughening amount; reversing the order will lead to several futile rounds of troubleshooting.
Failure 2: Strong odor inside the car after being exposed to sunlight. The root cause is not just the material. A public case is worth remembering for everyone in interior manufacturing: in a certain supply chain, 'modified PP pellets passed odor testing, but the final plastic parts exceeded odor limits.' After tracking the industry chain, two reasons were found—excessive release agent sprayed during injection molding introducing off-odor, and too high injection molding temperature causing partial decomposition of the material, generating odor. The conclusion of the paper is: to thoroughly solve the odor problem in plastic parts, car manufacturers, component companies, and raw material suppliers must work together. Blaming the material supplier alone is the most common mistake in this industry.
Failure 3: The warm air duct softens and deforms after being warm for a long time. The root cause is the misuse of regular PP with insufficient heat resistance, or the actual operating conditions consistently exceeding the 140℃ heat load that toughened PP can withstand in the short term. Toughened PP being able to handle short-term peaks does not mean it can endure long-term overheating—this point needs to enter the reverse honesty section.
Ineffective point four (daring to deny the strongest one): adding fiberglass to the air duct thinking it makes it 'stronger.' The material library lists 'air conditioning ducts / air guide covers / fan blades' in the same row, all marked as PP-GF20/GF30, but this mixes 'supply ducts' and 'structural components' in one line. Air ducts require flexibility and noise reduction; adding fiberglass increases rigidity, reduces damping, and may even introduce abnormal noise and surface fibers—the approach is completely wrong. The main body of the duct should not have fiberglass; components that need stiffness and creep resistance are the air guide cover and fan blades, which are suitable for fiberglass reinforcement. Using the fiberglass material meant for fan blades on ducts will ruin both appearance and acoustic performance.
5. Verification sequence: what is a priori, what is a posteriori
Almost no one in the industry writes this section, but it is key to whether changing materials can save money and whether the smell can pass inspection. If the order is wrong, problems will only appear the moment of loading.
`
① Sample physical comparison Four odor tests (VDA 270/275/277/278) Notch impact MFR Shrinkage rate
↓ All eight items must be within the threshold before proceeding
② Dual smell testing: first test the smell of the particles, then test the smell of the parts (lesson from public cases: particle passed ≠ part passed)
↓ If any item exceeds the standard, first determine whether it is the material or the process
③ Process Window Verification Maximum Material Temperature Residence Time Release Agent Usage Drying Conditions (for making process test pieces)
↓ In this step, lock the two causal chains 'release agent / material temperature' into the verification checklist
④ Short shot mold test: Check whether the filling is complete, weld lines/floating fibers, and inner wall appearance
↓ Only after the short-range shot works can we talk about mass production
⑤ Loading Match Buckle assembly force, gaps, actual vehicle odor
↓
⑥ Batch Trial Production Client-side Verification
`
Text version of the conclusion: The verification sequence is: Sample → Dual odor test → Process window → Short shot → Machine matching → Batch. The dual odor test must be completed before mold trials, as it is the most decisive; the process window (material temperature / release agent / drying) must be included in the verification checklist, otherwise odor issues after machine loading can never be traced to the root.
6. Reverse Honesty: In these three situations, the air duct should not be reinforced with modified PP.
Earlier we talked about 'how to do it'; here we talk about 'when not to do it.' This section has the highest value for selection and judgment.
| The situation that occurred | Why modified PP is not suitable | Which way should I go? |
|---|
| Requires long-term operating temperature above 150℃ (long-term overheating of warm air) | Toughened PP can withstand a short-term thermal load of 140℃, but if exposed to long-term over-temperature, its load deformation temperature cannot hold up. Even enhancing it through fillers has its limits. | Replace with higher heat-resistant engineering plastics or heat-resistant modified systems |
| Use the air duct as a high-rigidity load-bearing structure | The air duct itself doesn’t bear any load; if you insist on rigidity, you need to add fiberglass, but that would sacrifice flexibility and noise reduction, which is the wrong approach. | Structural components and air ducts are designed separately, and the load-bearing section uses glass fiber reinforced PP. |
| Requires extremely high surface gloss while eliminating the need for painting | Highlight spray-free requirements call for a fine surface with little filler, which is compatible with low-filling orientation of low-odor systems, but conflicts with the main line of 'flexible noise reduction' in the air duct, and the odor threshold remains the same. | The surface parts go through a dedicated spray-free scratch-resistant system, and the odor threshold cannot be compromised. |
The pattern is very clear: whenever 'two opposite requirements must be met at the same time' appear, it indicates that this part should not be forced with PP. In such cases, our approach is to first clarify this point, and then discuss whether there is a compromise—forcing the current orders will ultimately result in rework and claims to be returned.
7. What to touch when changing materials: a checklist to look at first before taking action
Before deciding to try modifying the PP, it is recommended to 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 difference in shrinkage rate of the new material compared to the original plan is particularly sensitive in long parts | The dimensions are out of tolerance, the clips do not align, and the assembly gaps are off. |
| Gate and Venting | High MFR flow differences in low-odor materials; long air ducts require sufficient venting to prevent trapped air | Underfilling, air entrapment, inner wall defects |
| Material Temperature and Mold Temperature | Toughening-related thermal stability window is narrow (corresponding to the VW temperature chain) | Excessive material temperature causes decomposition odor and surface defects |
| Dry | Low-odor materials usually need to be dried to remove moisture and volatiles (which directly affect the odor) | If not dry, the aroma rises, silver threads |
| Pressure Holding and Demolding | Demolding force of flexible material / flashing; excessive use of release agent introduces off-flavors (corresponding to VW release agent chain) | Deformation, ejection strain, excessive part odor |
| Color difference | The inner wall is visible, and the color board must be confirmed before starting the machine. | Batch color difference dispute |
| Verification order | Sample → Dual odor test → Process window → Short shot → Loading matching | All the risks are concentrated to explode at the final step |
Text-based conclusion: Material changes involve three aspects: molds, processes, and color differences. The most important to discuss first are the verification sequence and process window. Skipping small samples and going straight to mold testing is equivalent to spending the cost upfront; skipping odor double-checks and process windows and going straight to mass production means that a single failure will require reworking the entire batch for odor issues.
8. One-page report sheet (can be directly pasted into PPT)
| Scene | Recommended Route | Key indicators | Verification standard | Conditions that need to be confirmed first |
|---|
| Conventional air conditioning duct | Impact Copolymer PP Toughened Low Odor System | Odor four items VDA threshold; buckle flexibility allowance; MFR medium-high | VDA 270/275/277/278; GB/T 1043.1; GB/T 3682.1 | Molding method, assembly / welding method |
| Warm air duct (contact warm air) | Toughened PP (short-term 140℃) | Short-term heat resistance 140℃; odor four-item pass | Short-term heat aging Heat resistance test; VDA four items | Actual temperature of warm air, whether it is above 140℃ for a long time |
| Silent / Major Transformation Segment | Elastomer system (high proportion of TPO/POE) | Damping / Flexibility / Fatigue Resistance | Impact according to the applicable temperature range per item | Mute requirement level, deformation amount |
| Wind guide cover / fan blades (for comparison, not in this route) | Glass Fiber Reinforced PP GF20-30 | Stiffness, creep resistance, HDT | — | Explain that the air duct and structural parts are two separate sets of materials |
Text-based conclusion: The purpose of this table is to allow technicians to report conclusions directly without having to reorganize the language. There is only one criterion for judgment—whether the customer can decide on the direction of the materials in one meeting using this table. The air duct and the air guide hood, and the fan blades are two separate logics, do not mix them when making selections.
9. The part of this piece that is most prone to problems is often not the material.
The two most common failure types in the air duct and heater hose industry are: one, assembly clip cracking (insufficient flexibility); and two, interior odor after sun exposure (low-odor properties not maintained). Public cases have recorded that modified PP pellets passed odor testing, but the final plastic parts still exceeded odor limits. Following the industry chain, the causes were traced to two causal chains—excessive mold release agent sprayed during injection molding introducing off-odor, and local decomposition of material due to excessive injection molding temperature producing odor. The conclusion of the papers is that material suppliers, component manufacturers, and OEMs must collaborate to completely solve the issue. This explains the 'causation' clearly: particles passing the test is one threshold, part compliance is another threshold, and the second threshold is restricted by the process, not the particles.
The commonly referenced German VDA standards in the industry include four items: odor ≤ level 3 (VDA 270), formaldehyde ≤ 10 mg/kg (VDA 275), condensable components ≤ 2 mg (VDA 278 / DIN 75201), and total carbon TVOC ≤ 50 μgC/g (VDA 277). Note that this is the OEM's control standard for modified particles, not a national standard. It must be written into the technical agreement in the order to be effective.
The common material route is impact-resistant copolymer PP as the base, toughening, and a low-odor additive system. The main body typically does not include glass fiber (which affects surface fiber appearance, damping, and noise reduction); at most, a small amount of talc is added to adjust dimensions. The balance between flexibility and low odor relies on a low-volatility toughening phase, low-odor stabilizers and color masterbatch, as well as controlling injection molding temperature limits, residence time, amount of release agent, and drying conditions.
Ningbo Kolon New Materials Co., Ltd. commonly supplies materials for this part in the direction of impact-resistant copolymer polypropylene – toughened – low odor system. The MFR is classified according to molding method, mainly used to address the two issues mentioned above: 'buckle flexibility' and 'odor passage'; for silent/large deformation sections, the corresponding direction is the elastomer system, which is coordinated separately as needed.
Frequently Asked Questions
Question: Can fiberglass be added to the air duct to make it stronger?
Answer: No, it shouldn't. Ducts require flexibility and noise reduction, while fiberglass increases rigidity and reduces damping, and may also cause abnormal sounds and floating fibers on the inner wall. Components that need stiffness, like air guides and fan blades, use fiberglass-reinforced PP, which is a different material. Using the material from structural parts for ducts would ruin both the appearance and the quietness.
Question: The particle odor meets the standards, but what should be done if the parts exceed the limit?
Answer: First, check the injection molding process—the amount of release agent and the maximum material temperature are the two most common culprits. Include these two factors along with the drying conditions in the verification checklist, have the material supplier provide the maximum material temperature and release agent recommendations, the parts manufacturer control the process, and the OEM set the limits and accept them; only with the cooperation of all three parties can it be managed properly.
| Operating condition | Key criterion | Cologne regular supply |
|---|
| Air conditioning duct / Heating duct | Odor four items VDA pass; buckle flexibility; short-term heat resistance 140°C | Impact copolymer PP Toughened Low-odor system direction, MFR classified according to molding |
| Silent / Major Transformation Segment | Damping / Flexibility / Fatigue Resistance | For the elastomer system (TPO/POE) direction, connect as needed |
Just a reminder: when a part has a problem, the most common mistake is to change the material first. If the clip breaks or the smell is strong—is it because the base material grade is wrong, the toughening amount is insufficient, or too much mold release agent was sprayed, or the material temperature spiked? The cause can't be determined accurately, and after changing several batches of material, the problem remains the same.
Ten, Lastly, Say Three Sentences
First, the first thing to consider when selecting a duct material is not "which material is best," but rather "how to balance flexibility and low odor." In six-dimensional working conditions, compliance is a hard requirement, temperature is the baseline, and snap-fit load is for assembly of a hard door; only by looking at all three together can the base material be determined.
Second, toughening and low odor share the same base material, yet they restrict each other. Toughened materials have poor thermal stability, and high processing temperatures lead to decomposition and odor; low-odor systems need to suppress all additive volatilization. Formulation involves prioritization, not simply stacking materials.
Third, the verification sequence is more important than the verification items. Small sample → dual odor test → process window → short shot → vehicle fit; particle compliance does not equal part compliance, and the cause-effect chains of mold release agent and material temperature must be included in the verification checklist.
The next article will discuss another automotive functional component—the radiator water tank and expansion box: the logic of that material is completely different, involving "long-term high temperature, coolant immersion, and pressure cycling" all combined.
About Us
What we deliver is not just a bag of material.
It also includes a judgment on material usage, a corresponding physical property sheet, and a contact person if issues arise.
Ningbo Kolon New Materials Co., Ltd. produces modified polypropylene (PP) granules in-house, covering three grades of base materials: homopolymer / random copolymer / impact copolymer, with modifications such as filled, glass fiber reinforced, toughened, flame retardant, low odor/low VOC, weather-resistant, and scratch-resistant paints; we also trade PP resins from major petrochemical plants, off-grade materials, and bulk materials.
