汽车门板立柱用什么改性PP？免喷涂耐划伤的答案不在"哪种料好"，在四道门槛：工况六维、三条路线、VW PV3952 划痕门限、验证顺序。这篇把划痕发白、应力发白、酰胺类与超高分子量硅氧烷一次讲清，并说明哪三种情况该换料。
"门板上这道划痕，洗了三次车还在，阳光下白得扎眼。"
这是我被问到门板立柱免喷涂时，最常听到的一句话。问的人多半是做内外饰的工程师，手里已经有一版免喷涂料，但装车评审时被划痕发白卡了回来。
门板立柱这类件走免喷涂，用的是改性PP体系，最怕的不是强度不够，是表面经不起碰。划痕发白、色差、应力发白，这三件事里任意一条不过，件就回炉。下面按工况、路线、判据、失效、验证五层往下拆。
同行抄不走的一个判断：门板立柱的免喷涂，划痕判据看的是"件用在哪儿"，不是"料好不好"。内饰件可以用酰胺类爽滑剂，外饰件用酰胺类是必错的——这一句后面会展开讲。
一、工况六维拆解：四个数字先报齐
门板立柱的工况，拆成六个维度报齐，方向就清楚。这一维里，改性PP门板立柱的耐温区间、服役时长、外观门限都能落到具体数。
| 维度 | 门板立柱的实际工况 | 对材料的要求 |
|---|
| 温度 | 车厢内常处 −20℃ 到 85℃；外饰立柱（如车门外板嵌条）夏季暴晒表面更高 | 内饰件耐温要求较缓；外饰件要扛热老化 |
| 载荷 | 以按压、扶手借力、储物挤压为主，冲击远低于保险杠 | 卡扣与装配韧性，不是高刚性 |
| 介质 | 汗液、清洁剂、内饰护理剂；外饰件还有雨水、洗车剂、融雪盐 | 耐化学 + 表面不被介质侵蚀发白 |
| 寿命 | 整车生命周期，常见按 10 年 / 15 万公里级设计 | 长期老化后划伤与发白不恶化 |
| 外观 | 免喷涂直接出 A 级或准 A 级表面，划痕 ΔE 要压住 | 划痕 dL、应力发白、色差 |
| 合规 | 低气味低 VOC、车内空气质量、回收与禁用物质 | 低气味体系 + 禁用物质管控 |
六个维度里，外观这一维是门板立柱免喷涂的"一票否决"线。其它维度出问题多是返工，外观过不了是整车评审直接打回。
内行细节：划痕的 dL 值对测试温度极敏感。同一块样板，23℃ 和 40℃ 下划出来的 dL 能差出一截——所以划痕评价必须锁死温度窗口，否则不同实验室给出来的数没法比对。
文字版结论：门板立柱免喷涂的工况，温度、载荷、寿命、外观四维也都能给出具体数字（−20~85℃、10 年 / 15 万公里、dL < 1.5、应力发白不可见），这四项是先报齐的硬指标。介质与合规两维决定助剂体系能不能用酰胺类。
二、材料路线对比：门板立柱的免喷涂三条路
门板立柱做免喷涂耐划伤，行业上主要三条路并列，没有"谁更好"，只有"对不对得上工况"。改性PP在这里是底子，决定表面体系怎么搭。
| 路线 | 拿到什么 | 代价 |
|---|
| PP/EPDM-T20（橡胶增韧打底） | 韧性好、抗白痕、装配不裂；内饰门板主流底子 | 刚性靠填料补，表面细腻度受填料量限制 |
| PP/PE-TD16（PP/PE 合金） | B 级车常用，加 5–8 份滑石粉调收缩，成本低 | 刚性一般，外观件需配抗刮体系 |
| 免喷涂 + 耐划伤表面体系 | 直接出件不喷漆，划痕 dL 可控；外饰走硅氧烷 | 表面体系成本较高，色板确认流程长 |
三条路怎么分：内饰门板以 PP/EPDM-T20 为主，要的是抗白痕和装配韧性；B 级车成本敏感用 PP/PE 合金；只要件走免喷涂、又要求表面耐划，就必须再叠一层耐划伤表面体系。
敢否定一个常见做法：有人为了降成本，把免喷涂外饰立柱直接套用内饰的酰胺类爽滑剂。这是必错的。酰胺类在 UV 下分解、超过 80℃ 热敏、还会迁移成油膜吸灰、被雨水洗车冲掉，对滑石粉填充体系基本无效。外饰件该走超高分子量硅氧烷。
文字版结论：门板立柱的免喷涂，基材和表面体系是两件事。基材解决韧性与收缩，表面体系解决划痕与发白；把表面体系省掉只调基材，划痕门限永远过不了。
三、★ 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好的一张。注意第四列"验证方法 · 标准号"——选型卡住的通常不是"看哪个指标"，而是"拿什么测、测到多少算过"。改性PP门板立柱的判据，划痕与发白各占一道。
| 指标 | 门限值（典型） | 验证方法 · 标准号 | 常见失效 | 通行解法 |
|---|
| 拉伸屈服应力 | ≥20 MPa | GB/T 1040.2 | 装配受力处开裂 | 基材档位 + 滑石粉补刚性 |
| 弯曲模量 | ≥1400 MPa | GB/T 9341 | 软塌、面差超差 | 滑石粉 15–40% 调刚性 |
| 缺口冲击强度 | ≥10 kJ/m² | GB/T 1043.1 | 卡扣装配开裂 | EPDM 增韧体系 |
| 划痕 dL | <1.5（低于 1.0 更理想） | VW PV3952（Erichsen 划痕仪，载荷 10N，φ1mm 划针，网格 2mm，划速 1000 mm/min，23±5℃；至少测 5 点取平均） | 划痕发白 | 超高分子量硅氧烷表面体系 |
| 应力发白 | 落球试验不得出现可见应力发白 | PV3966（落球试验） | 装配/外应力发白扩展 | 抗白痕体系 + 控内应力 |
文字版结论：这张表里划痕 dL 是门板立柱免喷涂的"主判据"，门限来自 VW PV3952，载荷 10N、划针 φ1mm、至少测 5 点取平均，低于 1.0 更理想。应力发白用 PV3966 落球另验一道——只验划痕不验落球，是漏项。
四、常见失效与根因：四处踩坑，一处敢否定
先放一张各家主机厂的划痕评价方法对照，它是失效归因的尺子。
| 标准 | 方法 | 验收门限 |
|---|
| Ford BN108-13（五指划痕） | 五支划针，载荷 2N–7N | 2N 划痕不可见；3N 不可见长度需 >30% |
| VW PV3952 | Erichsen 划痕仪，载荷 10N，划针 φ1mm、网格 2mm、划速 1000 mm/min、23±5℃ | dL < 1.5（低于 1.0 更理想），至少测 5 点取平均 |
| PV3966 | 落球试验（应力发白） | 不得出现可见应力发白 |
| PSA / Renault D44 1900 | 砂纸划纹理样板一次 | dL < 2 且灰度 ≥3 |
| SAE J400 | 碎石冲击（Gravelometer） | — |
| 户外件附加 | UV + 热老化 | 500–1000 h 后耐划伤性能不下降 |
来源：A 级——WO2015070360 专利说明书（完整引用 PV3952 测试参数）；B 级——Evonik 技术资料、湘西化工技术文。写作口径：列的是主机厂通行评价方法，不是国家标准。
文字版结论：划痕评价不是一道题，是五道以上。内饰用 Ford BN108-13 或 VW PV3952，外饰还要过 PSA D44 1900 的砂纸纹理与 SAE J400 碎石冲击，户外件再叠加 UV + 热老化 500–1000 h。只做一种划痕测试就交差，是最典型的漏项。
失效一：划痕发白。根因多半不是基材脆，是表面耐划体系选错——内饰用了外饰才该用的硬体系，或外饰错用了酰胺类。先定件归属（内/外饰），再定表面体系。
失效二：应力发白。门板在装配与外应力下出现发白并随时间扩展。根因是件的内应力没控住，或没上抗白痕体系。PV3966 落球试验不过，说明材料抗应力发白能力不足。
失效三：色差。免喷涂件色差先看色母与批次，再看注塑工艺。同一色板不同批次差一档，装车就露怯。色板必须先确认再上机。
失效四：耐光老化褪色。门板立柱长期受光，尤其外饰立柱。根因是色母与耐候体系没匹配，不是基材问题。
敢否定一个常见做法：把耐划伤只看划痕一道、不验应力发白。很多方案拿一块样板只做划痕，dL 压住了就交差，装车一受力应力发白全出来。划痕和落球（PV3966）是两套机理，必须同时过。
五、验证顺序：先验什么，后验什么
这一段同行几乎没人写，却是换改性PP能不能省钱的关键。顺序错了，问题会压到最后一步集中爆。
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① 小样物理比对 拉伸 / 弯曲 / 缺口冲击 / 收缩率 / MFR
↓ 五项都在门限内，才往下走
② 划痕与发白验证 VW PV3952（dL，测 5 点）+ PV3966（落球应力发白）
↓ 两道都过，再谈上机
③ 短射试模 看充填完整度、熔接线位置、表面浮纤
↓ 短射走通，才进批量
④ 装车匹配 间隙、色差、装配力、实车划痕抽检
↓
⑤ 批量试产 + 客户端验证
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文字版结论：验证顺序是 小样 → 划痕/发白 → 短射 → 装车匹配 → 批量。划痕与应力发白这两关必须放在试模之前过，因为它们最易一票否决；过了再做模具侧的事，才不会白花试模费。
六、反向诚实：这三种情况别用改性PP硬撑
前面讲"怎么做"，这里讲"什么时候别做"。这一段对选型的判断价值最高。
| 出现的情况 | 为什么改性PP不合适 | 该往哪走 |
|---|
| 同时要求 A 级表面 + 免喷涂 + 高刚性 | 免喷涂要表面细腻少填料；高刚性要高填充，两方向对拉 | 表面件与结构件分开设计，或换材料 |
| 外饰件用酰胺类耐划伤体系 | 酰胺类 UV 分解、>80℃ 热敏、迁移吸灰、被冲掉、对填料无效 | 直接改用超高分子量硅氧烷体系 |
| 要求长期工作温度 150℃ 以上 | 改性PP 负荷变形温度上限就在那条线附近，填充增强往上抬也有边界 | 换更高耐热的材料体系 |
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。遇到这种需求，先说清楚再谈折中——硬接下来的单子，最后都要用返工还回去。
七、换料风险清单：先看再动
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，装车间隙对不上 |
| 浇口与排气 | 免喷涂件对浇口位置和排气更敏感 | 流痕、气纹、表面缺陷 |
| 料温与模温 | 表面体系对工艺窗口敏感 | 表面浮纤、划痕门限掉 |
| 干燥 | 填充料通常不需；看具体体系 | 银丝、气泡 |
| 保压与脱模 | 收缩差异带来变形与顶白 | 变形、顶出拉伤 |
| 色差 | 免喷涂件必须先确认色板再上机 | 批次色差争议 |
| 验证顺序 | 小样 → 划痕/发白 → 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。跳过小样直接试模，等于把成本提前花出去；跳过短射直接批量，一次失败就是整批损失。
八、一页纸汇报对照表：直接贴进评审会
| 场景 | 推荐路线 | 关键指标 | 验证标准 | 需先确认的条件 |
|---|
| 内饰门板（免喷涂） | PP/EPDM-T20 + 硅氧烷表面体系 | 划痕 dL <1.5；应力发白不可见 | VW PV3952 + PV3966 | 内/外饰归属、色板 |
| 立柱饰板（薄壁） | 低填充高熔体强度 PP | 包覆贴合、低翘曲 | 装车匹配 | 包覆材料、壁厚 |
| 外饰立柱（耐候） | PP/PE 合金 + 硅氧烷 + 耐候 | dL <1.5；UV 后不劣化 | VW PV3952 + UV/热老化 500–1000 h | 户外服役条件 |
| B 级车成本件 | PP/PE-TD16 + 5–8 份滑石粉 | 收缩率、刚性 | GB/T 1040.2 / 9341 | 成本目标、外观等级 |
文字版结论：这张表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，能不能在一次评审里把材料方向定下来。
九、这个件上最容易出问题的，往往不是料
门板立柱免喷涂件上行业最常见的早期失效是划痕发白与应力发白，而这两类问题里，由材料本身引起的比例并不高。公开资料里记录过一组主机厂的划痕评价方法：VW PV3952 用 Erichsen 划痕仪、载荷 10N、划针 φ1mm、网格间距 2mm、划速 1000 mm/min、23±5℃ 下评价，门限 dL < 1.5（低于 1.0 更理想），至少测 5 点取平均；Ford BN108-13 用五指划痕、载荷 2N–7N，要求 2N 划痕不可见、3N 划痕不可见长度 >30%；PSA/Renault D44 1900 用砂纸划一次纹理样板，要求 dL < 2 且灰度 ≥3；户外件还要过 SAE J400 碎石冲击，以及 UV + 热老化 500–1000 h 后耐划伤不下降。
行业通行的判据很清楚：内饰件可以用酰胺类爽滑剂，外饰件用酰胺类是必错的。酰胺类（芥酸酰胺/油酸酰胺）成本低，但 UV 下分解、>80℃ 热敏、迁移过快形成油膜吸灰、雨水洗车会冲掉，而且对滑石粉/矿物填充体系无效；超高分子量硅氧烷热稳定到 300℃、UV 稳定、不迁移、不被冲掉、可同时抗应力发白。
关键不在"谁的料更滑"，在基材档位、填料比例、表面体系三件事能不能同时对上。
宁波市科隆新材料有限公司在这个件上常供的是改性聚丙烯（PP）粒子里的免喷涂耐划伤方向，按件的内/外饰归属给到对应的基材档位与表面体系，主要用来解决上面说的"划痕发白与应力发白"这两件事；配方按件的工况调，可以配合做小样比对与试模，件级客户多品种小批量的需求也能接。
常见问答
问：内饰 PP 的典型配方大概怎么配？
答：公开资料（Evonik）给过一版内饰 PP 典型配方：PP 共聚（+TPO）48–78%、色母 2–5%、滑石粉 15–40%、抗刮剂 2–4%、其他助剂 1%。这版比例说明一件事——抗刮剂只是其中一小份，基材与填料才是底子，表面体系另算。
问：外饰件能不能为了省钱用酰胺类？
答：不能。外饰件在 UV、雨水、洗车、>80℃ 环境下，酰胺类会分解、迁移、被冲掉，划痕门限很快失守。外饰件走超高分子量硅氧烷，是这条线上的通行做法，不是可选项。
| 工况 | 关键判据 | 科隆常规供应 |
|---|
| 内饰门板（免喷涂） | 划痕 dL <1.5（VW PV3952，10N）；应力发白不可见（PV3966） | 免喷涂耐划伤改性 PP，内饰走适配体系 |
| 外饰立柱（耐候） | dL <1.5；UV + 热老化 500–1000 h 后不劣化 | 免喷涂耐划伤改性 PP，外饰走硅氧烷体系 |
| 立柱饰板（薄壁） | 包覆贴合、低翘曲 | 低填充高熔体强度 PP 方向 |
想提醒一句：件出问题，最常见的错法是先换料。划痕发白、应力发白、色差——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。
最后说三句
第一，门板立柱免喷涂的主判据是划痕 dL，门限来自 VW PV3952（10N、φ1mm、测 5 点取平均，<1.5，低于 1.0 更理想），应力发白另用 PV3966 落球验一道。
第二，内饰件可以用酰胺类，外饰件用酰胺类是必错的——超高分子量硅氧烷热稳定到 300℃、UV 稳定、不迁移、可同时抗应力发白。
第三，验证顺序比验证项更重要。小样 → 划痕/发白 → 短射 → 装车匹配，划痕与应力发白两关必须放在试模之前过。
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What modified PP is used for car door panels and pillars? The answer to scratch-resistant coatings is not 'which material is good,' but lies in four thresholds: six-dimensional working conditions, three routes, VW PV3952 scratch limits, and verification sequence. This article explains in one go about scratch whitening, stress whitening, amide types versus ultra-high molecular weight siloxane, and also outlines in which three situations the material should be changed.
The scratch on the car door panel is still there even after washing the car three times, glaringly white in the sunlight.
This is the sentence I hear most often when asked about door panels and pillars that are exempt from painting. Most of the people asking are engineers working on interior and exterior trims, who already have a version of the paint-free coating, but it was sent back during the vehicle review due to white scratches.
Parts like door panels and pillars go through the process without coating, using a modified PP system. The biggest concern isn't insufficient strength, but that the surface can't withstand impacts. Scratches turning white, color differences, and stress whitening—if any of these three occur, the part goes back to the re-melting stage. Below, we break down into five layers: working conditions, process route, criteria, failure, and validation.
A judgment that peers can't copy: For the paint-free door panel posts, the scratch criterion looks at 'where the part is used,' not 'whether the material is good.' Interior parts can use amide-type lubricants, but using amide-type on exterior parts is always wrong — this sentence will be explained further later.
1. Six-dimensional breakdown of working conditions: report the four numbers first
The working conditions of the door panel pillars can be broken down into six dimensions to report comprehensively, and the direction will become clear. In this dimension, the temperature range, service life, and appearance thresholds of modified PP door panel pillars can all be specified with concrete numbers.
| Dimension | Actual working conditions of the door panel upright | Requirements for the materials |
|---|
| Temperature | Inside the car compartment is usually between −20°C and 85°C; the exterior pillars (such as the trim on the outside of the car door) have even higher surface temperatures when exposed to summer sunlight | Interior parts have relatively moderate temperature resistance requirements; exterior parts must withstand heat aging. |
| Load | Mainly relying on pressing, using the armrest for leverage, and squeezing storage; the impact is far less than that of a bumper. | The snap-fit and assembly toughness, not high rigidity |
| Medium | Sweat, cleaners, interior care products; exterior parts are also exposed to rain, car wash detergents, and de-icing salt | Chemical resistant, the surface is not corroded or whitened by media |
| Lifespan | For the entire vehicle lifecycle, it is common to design for 10 years / 150,000 kilometers | Scratches and whitening do not worsen after long-term aging |
| Appearance | Achieve A-level or quasi-A-level surface directly without spraying, and the scratch ΔE must be controlled | Scratches dL, stress whitening, color difference |
| Compliance | Low odor, low VOC, in-car air quality, recycling and banned substances | Low-odor system Prohibited substance control |
Among the six dimensions, the appearance dimension is a 'veto line' for door panel and pillar surfaces that haven't been painted. Issues in other dimensions mostly result in rework, but if the appearance fails, the entire vehicle review is directly rejected.
Expert detail: The dL value of scratches is extremely sensitive to the test temperature. For the same sample, the dL measured at 23°C and 40°C can differ significantly—so scratch evaluation must lock the temperature window; otherwise, numbers from different laboratories cannot be compared.
Textual conclusion: For the condition where the door panel pillars do not require painting, specific numbers can be provided for temperature, load, lifespan, and appearance (−20~85℃, 10 years / 150,000 km, dL < 1.5, stress whitening not visible); these four are the hard indicators that must be reported first. The medium and compliance dimensions determine whether the additive system can use amides.
2. Comparison of Material Routes: Three non-painting options for door panel pillars
Door panel uprights are made scratch-resistant without spraying. In the industry, there are mainly three parallel approaches; there is no 'which is better,' only 'which suits the working conditions.' Modified PP serves as the base here, determining how the surface system is constructed.
| Route | Get what | Cost |
|---|
| PP/EPDM-T20 (Rubber toughening primer) | Good toughness, resistant to white marks, does not crack during assembly; mainstream base for interior door panels | Rigidity is supplemented by filler, and surface fineness is limited by the amount of filler |
| PP/PE-TD16 (PP/PE alloy) | Commonly used for B-class cars, add 5–8 parts talcum powder to adjust shrinkage, low cost | The rigidity is average, and the exterior parts need an anti-scratch system. |
| Paint-free Scratch-resistant Surface System | Direct parts delivery without painting, scratches dL are controllable; exterior finishes use silicone oxide. | The surface system is relatively costly, and the color board confirmation process is long. |
How to differentiate the three types of roads: interior door panels mainly use PP/EPDM-T20, targeting resistance to white marks and assembly toughness; cost-sensitive B-class cars use PP/PE alloy; if a part is spray-free but requires surface scratch resistance, an additional scratch-resistant surface system must be layered on.
Can we deny a common practice: some people, in order to reduce costs, directly use amide-based lubricants meant for interior trim on unpainted exterior pillars. This is definitely wrong. Amides decompose under UV, are heat-sensitive above 80°C, can migrate to form an oily film that attracts dust, and get washed away by rainwater, making them basically ineffective for talc-filled systems. Exterior trim should use ultra-high molecular weight silicones.
Text version conclusion: The spray-free treatment of door panel stiles, the substrate, and the surface system are two separate matters. The substrate addresses toughness and shrinkage, while the surface system addresses scratches and whitening; if you skip the surface system and only adjust the substrate, the scratch threshold will never be met.
3. ★ Selection Criteria Table: Five Indicators with Verification Methods
The table below is the one you should keep the most carefully in the entire article. Pay attention to the fourth column "Verification Method · Standard Number" — what usually gets stuck during selection is not "which indicator to look at," but "what to measure with and what value counts as passing." For the modified PP door panel pillar, the criteria assign one point each to scratches and whitening.
| Indicator | Threshold Value (Typical) | Verification Method · Standard Number | Common Failures | Common solution |
|---|
| Tensile yield stress | ≥20 MPa | GB/T 1040.2 | Cracking at the load-bearing assembly | Substrate grade Talc powder reinforcing rigidity |
| Bending modulus | ≥1400 MPa | GB/T 9341 | Soft and saggy, poor appearance, extremely poor | Talc 15–40% Adjust rigidity |
| Notch impact strength | ≥10 kJ/m² | GB/T 1043.1 | Snap-fit assembly cracking | EPDM toughening system |
| Scratch dL | <1.5 (below 1.0 is more ideal) | VW PV3952 (Erichsen scratch tester, load 10N, φ1mm stylus, grid 2mm, scratching speed 1000 mm/min, 23±5℃; measure at least 5 points and take the average) | Scratch turns white | Ultrahigh molecular weight silicone surface system |
| Stress whitening | No visible whitening due to stress should occur in the drop ball test | PV3966 (Drop Ball Test) | Assembly/External Stress Whitening Extension | Anti-whitening System Control Internal Stress |
Text version conclusion: In this table, the scratch dL is the "main criterion" for the door pillar without paint spraying. The threshold comes from VW PV3952, with a load of 10N, a scribe needle of φ1mm, measuring at least 5 points and taking the average; below 1.0 is preferable. Whitening due to stress is verified separately with PV3966 impact testing — only testing scratches without performing the impact test is a missing item.
4. Common Failures and Root Causes: Stumble everywhere, but can you deny even one place
First, let's put up a comparison of the scratch evaluation methods of various OEMs; it serves as a ruler for failure attribution.
| Standard | Method | Acceptance threshold |
|---|
| Ford BN108-13 (Five-Finger Scratch) | Five stylus needles, load 2N–7N | 2N Scratches not visible; 3N Invisible length must be >30% |
| VW PV3952 | Erichsen scratch tester, load 10N, scratch pin φ1mm, grid 2mm, scratching speed 1000 mm/min, 23±5℃ | dL < 1.5 (less than 1.0 is more ideal), measure at least 5 points and take the average |
| PV3966 | Drop Ball Test (Stress Whitening) | Visible stress whitening must not occur |
| PSA / Renault D44 1900 | Sandpaper scratch texture sample once | dL < 2 and grayscale ≥ 3 |
| SAE J400 | Gravel Impact (Gravelometer) | — |
| Outdoor Accessories | UV Thermal Aging | Scratch resistance does not decrease after 500–1000 hours |
Source: Level A — WO2015070360 patent specification (full citation of PV3952 test parameters); Level B — Evonik technical data, Xiangxi Chemical technical documents. Writing standard: The listed methods are commonly used evaluation methods by OEMs, not national standards.
Text version conclusion: Scratch evaluation is not a single test, but more than five. For interiors, use Ford BN108-13 or VW PV3952; for exteriors, also pass PSA D44 1900 sandpaper texture and SAE J400 gravel impact; for outdoor parts, additionally undergo UV and heat aging for 500–1000 hours. Only doing one type of scratch test and considering it done is the most typical omission.
Failure 1: Scratches turning white. The root cause is mostly not that the substrate is brittle, but that the scratch-resistant coating system was chosen incorrectly—interior parts used a hard system meant for exterior parts, or exterior parts mistakenly used amide-based materials. First, determine the part's classification (interior/exterior), then decide on the surface coating system.
Failure 2: Stress whitening. The door panel shows whitening under assembly and external stress, and it expands over time. The root cause is that the internal stress of the part is not controlled, or there is no anti-white mark system applied. PV3966 drop test fails, indicating that the material's resistance to stress whitening is insufficient.
Failure Three: Color Difference. For color differences in unpainted parts, first check the color masterbatch and batch, then look at the injection molding process. Even a one-level difference between the same color sample but different batches will show when assembled onto the car. The color sample must be confirmed before starting the machine.
Failure 4: Light aging and fading. Door panel posts are exposed to light for a long time, especially exterior decorative posts. The root cause is that the color masterbatch is not compatible with the weather-resistant system, not a substrate problem.
Can one deny a common practice: only looking at scratch resistance by scratches alone, without testing for stress whitening. Many proposals only test one sample for scratches, and if dL holds, they consider it done, but once installed and stressed, stress whitening fully appears. Scratches and falling ball (PV3966) are two separate mechanisms and must both pass.
5. Verification sequence: what is a priori, what is a posteriori
Almost no peers write this part, yet it is the key to whether using modified PP can save money. If the order is wrong, the problem will all concentrate and explode at the final step.
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① Sample Physical Comparison Tensile / Bending / Notch Impact / Shrinkage / MFR
↓ Only proceed if all five items are within the threshold
② Scratch and whitening verification VW PV3952 (dL, measure 5 points) PV3966 (whitening under impact stress)
↓ Pass both questions before talking about going on the computer
③ Short-shot mold trial Check filling completeness, weld line position, surface fibering
↓ Short-shooting is cleared before moving on to batch production
④ Loading Match Gaps, color difference, assembly force, spot check for scratches on the actual vehicle
↓
⑤ Batch trial production Client-side verification
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Text version conclusion: The verification sequence is sample → scratches/whitening → short shots → loading match → batch. The scratches and stress whitening stages must be checked before mold trials, because they are the easiest to reject outright; once passed, then proceed with mold-side tasks to avoid wasting mold trial costs.
6. Reverse honesty: Don't force modified PP in these three situations
Earlier we talked about 'how to do it'; here we talk about 'when not to do it.' This section has the highest judgment value for selection.
| The situation that occurred | Why is modified PP not suitable | Which way should I go? |
|---|
| At the same time, requires A-level surface, no coating, high rigidity | No coating requires a fine surface with little filler; high rigidity requires high filling, with tensile tests in two directions. | Design the exterior parts and structural parts separately, or change the material |
| Amide-based scratch-resistant system for exterior trim | Amide UV decomposition, >80℃ thermal sensitivity, migration dusting, washed away, ineffective on fillers | Directly switch to an ultra-high molecular weight siloxane system |
| Requires a long-term operating temperature above 150℃ | The upper limit of the heat deflection temperature of modified PP is around that line, and the enhancement from filling also has a boundary when raised. | Switch to a material system with higher heat resistance |
Consistent pattern: Whenever there is a 'requirement for two opposite directions at the same time,' it indicates that this part should not be forcibly made with PP. When encountering such a demand, clarify it first before discussing a compromise—if you forcibly proceed with the order, it will ultimately have to be reworked and returned.
7. Material Change Risk List: Look Before Acting
Before deciding to try modifying PP, it is recommended to go through this table first. The customer's real concern is often not performance, but 'whether I need to change my current mold and process'.
| 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 off, and the assembly gap does not align. |
| Gate and Venting | Spray-free parts are more sensitive to gate location and venting | Flow marks, gas patterns, surface defects |
| Material Temperature and Mold Temperature | The surface system is sensitive to the process window | Surface floating fibers and scratch threshold dropped |
| Dry | Filler is usually not needed; it depends on the specific system. | Silver threads, bubbles |
| Pressure Holding and Demolding | Shrinkage differences cause deformation and whitening on the surface | Deformation, extrusion strain |
| Color difference | Non-painted parts must be confirmed with the color sample before being put on the machine | Batch color difference dispute |
| Verification order | Sample → Scratch/Whitening → Short Shot → Loading Match | All the risks are concentrated to explode at the final step |
Text version conclusion: Material change involves three aspects: molds, processes, and color differences, among which the verification sequence should be discussed first. Skipping small samples and testing the mold directly is equivalent to spending the cost in advance; skipping trial shots and going straight to mass production can result in the loss of the entire batch if it fails once.
8. One-page report comparison table: directly paste into the review meeting
| Scene | Recommended Route | Key indicators | Verification Standard | Conditions that need to be confirmed first |
|---|
| Interior door panel (paint-free) | PP/EPDM-T20 Silicone Surface System | Scratch dL <1.5; stress whitening not visible | VW PV3952 PV3966 | Interior/Exterior Ownership, Color Swatch |
| Column trim panel (thin-walled) | Low-fill, high melt strength PP | Coating fit, low warpage | Loading Match | Coating material, wall thickness |
| Exterior trim pillar (weather-resistant) | PP/PE alloy Silicone Weather resistance | dL <1.5; no deterioration after UV | VW PV3952 UV/thermal aging 500–1000 h | Outdoor Service Conditions |
| B-class car cost parts | PP/PE-TD16 5–8 parts talcum powder | Shrinkage rate, rigidity | GB/T 1040.2 / 9341 | Cost targets, appearance grades |
Text version of the conclusion: This table allows technicians to report the conclusions directly without having to reorganize their wording. There is only one criterion for judgment — whether the customer can use this table to finalize the material direction in a single review.
9. The part of this item that is most prone to problems is often not the material.
The most common early failures in the industry for door panel upright columns that do not require painting are scratch whitening and stress whitening, and the proportion caused by the material itself in these two types of problems is not high. Public data records a set of scratch evaluation methods from OEMs: VW PV3952 uses the Erichsen scratch tester, load 10N, scratch needle φ1mm, grid spacing 2mm, scratching speed 1000 mm/min, evaluated at 23±5℃, with a threshold dL < 1.5 (preferably below 1.0), measuring at least 5 points and taking the average; Ford BN108-13 uses the five-finger scratch test, load 2N–7N, requiring 2N scratches to be invisible and the length of 3N scratches to be invisible to exceed 30%; PSA/Renault D44 1900 uses sandpaper to scratch the texture sample once, requiring dL < 2 and grayscale ≥3; outdoor parts also need to pass SAE J400 gravel impact tests, and after 500–1000 hours of UV and thermal aging, scratch resistance should not decrease.
The industry-standard criteria are very clear: amide-based lubricants can be used for interior parts, but using amides for exterior parts is definitely wrong. Amides (erucamide/oleamide) are low-cost, but they decompose under UV, are heat-sensitive above 80°C, migrate too quickly forming an oily film that attracts dust, can be washed away by rain or car washing, and are ineffective for talc/mineral-filled systems; ultra-high molecular weight siloxanes are thermally stable up to 300°C, UV-stable, non-migratory, not washed away, and can also resist stress whitening.
The key is not 'whose paste is smoother,' but whether the base material grade, filler ratio, and surface system can all match up at the same time.
Ningbo Kolon New Materials Co., Ltd. commonly supplies, for this component, modified polypropylene (PP) particles with scratch-resistant properties that do not require coating. According to whether the part is for interior or exterior decoration, the corresponding substrate grade and surface system are provided, mainly to address the previously mentioned issues of 'scratch whitening and stress whitening.' The formulation can be adjusted according to the working conditions of the part and can be used for small sample comparisons and trial molding. It can also meet the needs of part-level customers for multiple varieties in small batches.
Frequently Asked Questions
Question: What is the typical formulation for interior PP?
Answer: Public information (Evonik) has provided a version of a typical interior PP formulation: PP copolymer (TPO) 48–78%, color masterbatch 2–5%, talc 15–40%, anti-scratch agent 2–4%, other additives 1%. This proportion shows one thing—a anti-scratch agent is only a small part, the base material and filler are the foundation, and the surface system is calculated separately.
Question: Can exterior trim parts use amides to save money?
Answer: No. For exterior parts, under UV, rain, car washing, and temperatures above 80°C, amides will decompose, migrate, and be washed away, and the scratch threshold will quickly be compromised. Using ultra-high molecular weight siloxane for exterior parts is the standard practice on this line, not an optional choice.
| Operating condition | Key criterion | Cologne regular supply |
|---|
| Interior door panel (paint-free) | Scratch dL <1.5 (VW PV3952, 10N); stress whitening not visible (PV3966) | Scratch-resistant modified PP without coating, interior follows the adaptation system |
| Exterior trim pillar (weather-resistant) | dL <1.5; UV thermal aging does not deteriorate after 500–1000 h | Scratch-resistant modified PP without spray coating, exterior uses a siloxane system |
| Column trim panel (thin-walled) | Wrapping fit, low warpage | Low-fill, high melt strength PP orientation |
I want to give a reminder: when there is a problem with a piece, the most common mistake is to change the material first. White scratches, stress whitening, color differences—each of these issues has more than one cause. Identify the cause first, then change the material; if you reverse the order, you often end up changing materials several times and still stay in the same place.
Finally, say three sentences
First, the main criterion for not painting the door panel pillar is the scratch dL. The threshold comes from VW PV3952 (10N, φ1mm, measure 5 points and take the average, <1.5, below 1.0 is more ideal). Stress whitening should be additionally checked using PV3966 drop ball test.
Second, interior trim parts can use amides, but it is definitely wrong to use amides for exterior trim parts—ultra-high molecular weight siloxane is thermally stable up to 300°C, UV stable, non-migrating, and can resist stress whitening at the same time.
Third, the verification order is more important than the verification items. Small sample → scratches/whitening → short shot → loading match, the scratches and stress whitening steps must be completed before trial molding.
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