工具手柄包胶用改性PP，成败不在软料，在界面。PP 是非极性材料，表面能只有 29-31 mN/m，二次注塑要在硬芯上直接包软层，界面附着力是第一道门槛。这篇把三种界面做法、九项判据、界面剥离要做三次的验证顺序，以及"哪四个条件同时出现就不该用 PP 基包胶"一次讲清。
手柄包胶这件事，客户问得最多的一句是："软一点，手感是不是就好了？"
我见过一个做电动工具的客户，把手柄软层硬度从邵氏 A65 降到 A45。握着确实软了，但售后投诉反而多了三条：湿手打滑、包胶边缘卷边、用半年软层被压得发亮发硬。
结论先给：包胶件的成败不在软料，在界面。 工具手柄包胶用改性PP，第一个要解决的不是软料，是那条只有几微米厚的界面。
硬度只是手感的一个维度；真正决定这个件能用多久的，是界面附着与软层在长期握持压下的回弹保持。
所以正确的第一句话是：先问粘得住粘不住，再问握得舒服不舒服。 下面按工况、界面、路线、判据、验证五层往下拆。
一、工况六维拆解：-40℃ 到 90℃、手汗与机油，包胶件的工况和结构件不是一个算法
包胶手柄的第一条载荷是"压"，不是"拉"；第一条介质是手汗，不是雨水。
把六个维度摆在一起看：
| 维度 | 工具手柄的实际工况 | 对材料的要求 |
|---|
| 温度 | 冬季户外 -40℃ 不冻硬；电动工具机身长时运行可到 90℃ | 软层耐温 -40~90℃；长期 80℃ 以上要重估 |
| 载荷 | 握持压（握力可达数百牛，单次很小）；1.5 m 跌落；电动工具持续振动 | 回弹保持 + 界面抗冲击 + 抗疲劳 |
| 介质 | 手汗（含盐与乳酸）、机油与润滑脂、切削液、清洗剂 | 耐汗、耐油、不溶胀不发粘 |
| 寿命 | 手柄是"一天八小时"的件，不是"偶尔用一次"的件 | 长期压缩后的厚度保持 |
| 外观与手感 | 哑光或纹路表面；干态与湿态摩擦系数；品牌件要求色标一致 | 湿态防滑 + 色差稳定 |
| 合规 | 阻燃（部分电气件）、手持电动工具安全、长期皮肤接触、食品接触（厨具柄） | 阻燃等级 + 迁移与色牢度 |
六维里，只有两维是一票否决性质的：界面和湿态摩擦。 其他维度出问题最多是体验差、返工；这两条出问题，一个是不合格，一个是安全事故。
一个内行细节：握持压其实非常小，小到用普通压缩试验都懒得做。但它是一天八小时的持续压。把软层压薄、压硬、压亮的，不是哪一次大力，是时间和次数。所以这个件真正该测的是压缩永久变形，不是拉伸强度。
二、界面这一关：PP 表面能只有 29-31 mN/m，三条路径与各自的代价
PP 难包，原因只有一个：它是非极性材料，表面能太低。
据公开资料（B 级），PP 的临界表面张力约 29-31 dyn/cm，而多数 TPE 体系在 40 dyn/cm 以上。两者极性不匹配，熔融的软料流经 PP 表面时形不成分子级浸润，冷却后界面留下一层微间隙——这就是"看着粘住了，一撕就开"的来源。
行业把这种情况叫假包胶：靠机械嵌合或范德华力勉强挂住。
据公开资料（B 级），剥离强度低于 2 N/mm 基本可判为假包胶；真正粘住的包胶件，180° 剥离强度应在 3 N/mm 以上。而且破坏模式必须是软层本体撕裂，不是界面分离。 这一条比数值更重要——它区分了"粘住"和"挂住"。
要让界面真粘住，行业上有三条路径，代价各不相同：
▸ 路径一 · 相容剂 / 增容层
拿到 ▸ 界面从物理嵌合变成化学过渡层。据公开资料（B 级），PP-g-MAH 添加 1-3%、或 SEBS-g-MAH 添加 2-3%，界面粘结强度可从 0.8 MPa 提到 1.5 MPa 以上；接枝率控制在 0.5%-1.5% 时，界面强度可提升 50%-80%。
代价 ▸ 多一道配方工作。相容剂过量会压流动性、抬高成本，还要和充油量一起配平——油加多了会迁移，反而削弱界面。
▸ 路径二 · 机械锁扣结构
拿到 ▸ 靠几何咬合兜底。结合面做微凹槽（深 0.15-0.3 mm、宽 0.5-1 mm）、边缘倒扣（30-45°、深 0.5-1 mm）、φ2-4 mm 贯穿孔做铆钉锁合，据公开资料（B 级），剥离力可提升 2-3 倍。
代价 ▸ 模具复杂；孔位与倒扣处应力集中，是后续开裂的高发点；外观自由度也受限。
▸ 路径三 · 换硬芯基材
拿到 ▸ 直接换到 PA、ABS、PC-ABS 这类极性硬芯，界面天生好做，料温窗口提到 190-230℃。
代价 ▸ 那就不是本篇的料了。 硬芯不再走 PP，这个件上 PP 基材的位置就用不上。这一条得老实说，不能为了让方案看起来完整而含糊过去。
界面这件事，软料解决一半，硬芯和结构解决另一半。 只盯着软料配方调硬度，是把问题看小了。
三、三条材料路线怎么分：PP + SEBS、换极性硬芯、TPU/硅胶/EPDM 的边界
路线不用争谁更好，看硬芯是什么料、耐温要多少、耐油耐磨要多少。
| 路线 | 拿到什么 | 代价 |
|---|
| PP 硬芯 + SEBS 基 TPE（含 PP 组分 / 接枝改性） | 免底涂、湿态防滑、耐油耐汗、-40℃ 不冻硬、可回收 | 必须先解决 PP 低表面能界面；长期耐温有上限 |
| PP 硬芯 + 纯 SEBS 基 TPE（未做 PP 适配） | 通用、价格友好 | 剥离仅 0.3-0.8 N/mm，属假包胶区间 |
| 换极性硬芯（PA / ABS / PC-ABS）+ 极性配方 TPE | 界面天生好做，料温窗口 190-230℃ | 硬芯材料换了，成本、吸湿、尺寸跟着来 |
| TPU 包胶 | 耐磨、耐油突出 | 以极性基材为主；手感偏硬，低温偏硬 |
| 硅胶包胶 | 亲肤、耐温耐候好 | 与 PP 不化学粘接，需底涂或机械结构；成本高 |
| EPDM 硫化包胶 | 耐候耐温好、原料成本低 | 靠硫化成型，周期长；与 PP 不以化学粘接为主 |
这里要说清一组最容易混的概念："TPE 包 PP"不是一个材料，是一类材料。
纯 SEBS 基 TPE 与 PP 之间只有弱相互作用，剥离强度典型在 0.3-0.8 N/mm；在 SEBS 基体里预先加入一定比例的 PP 树脂，熔融时 PP 组分与硬芯 PP 发生共结晶，剥离强度能到 2.5-4.0 N/mm；再在分子链上接枝马来酸酐（接枝率 0.5%-1.5%），靠化学键结合，可达 3.5-5.5 N/mm。
差别就在"有没有和 PP 共结晶的那一段"，不在于软不软。 很多客户拿着一支标着"包 PP 专用"的料来问为什么还是掉，答案常常是这一支只做了通用适配，没做共结晶或接枝。
三条路线是分工，不是替代：软层要极耐磨看 TPU；要耐温耐候看硅胶或 EPDM；要免底涂、湿态防滑、还能回收，走 SEBS 基 TPE 包 PP。改性PP 做硬芯、SEBS 基 TPE 做软层，是成本与工艺上比较顺的一组搭配，前提是界面那一关先过。
敢否定一个常见做法：手感发涩，就往软料里加爽滑剂（芥酸酰胺、油酸酰胺一类）。这是错的，而且错得很隐蔽。这类助剂会持续迁移到表面，在结合面上形成一层隔离膜，正好把界面强度毁掉。你在手感上加的那一点爽滑，就是脱胶的起点。要改善手感，该动的是表面纹路与硬度-厚度配合，不是加迁移型助剂。
四、★ 选型判据表：从界面剥离到湿态摩擦系数，九项怎么验
下面这张表是全篇最该收藏的部分，按改性PP 硬芯 + 软层包胶的组合开。注意第三列"验证方法"——这个件上最常卡住的不是"要看哪个指标"，是"拿什么测、测到多少算过、破坏长什么样算合格"。
| 指标 | 门限值（典型） | 验证方法 / 标准 | 常见失效 | 通行解法 |
|---|
| 180° 剥离强度（干态） | ≥3.0 N/mm，且破坏模式为软层本体撕裂 | GB/T 2790 / ISO 8510-1 / ASTM D903 | 界面剥离、边缘卷边 | 相容剂 + 基材预热 + 锚定结构 |
| 剥离强度（湿热老化后） | 95℃×2 h 水煮后衰减 ≤20% | GB/T 2790 + 水煮预处理 | 延迟脱层 | 低迁移油系 + 高接枝相容剂 |
| 剥离强度（冷热循环后） | 循环后无可见起泡与剥离 | GB/T 2790 + -40~85℃ 循环 | 浮纤区起泡、转角剥离 | 避浮纤 + 补极性组分 |
| 干态摩擦系数 | μ ≥ 0.8（较宽松口径 ≥0.5） | ASTM D1894 / GB/T 10006（注明对摩面） | 握不住、打滑 | 表面纹路 + 配方调摩擦 |
| 湿态（手汗/水）摩擦系数 | 衰减 ≤15%，湿态 μ 仍 > 0.5 | 同上 + 人工汗液或水润湿 | 湿手打滑 | 湿态防滑体系 |
| 邵氏硬度 A | 40-70（电动工具手柄常见 45-55） | GB/T 531.1 / ISO 7619-1，23±2℃ | 难发力或握久疲劳 | 硬度与厚度配合 |
| 压缩永久变形 | 压缩率 25%，70℃×22 h 后按件企标判定 | GB/T 7759.1 / ISO 815-1 / ASTM D395 | 软层变薄、握持力下降 | 回弹体系 + 厚度留量 |
| 撕裂强度 | ≥15 kN/m | GB/T 529 / ISO 34-1 | 裂口翻边 | 本体强度与硬度匹配 |
| 耐汗液与油脂 | 人工汗液 / 润滑油浸泡后色差与力学变化在门限内 | DIN 53160-2（人工汗液，pH 6.5）；介质浸泡 23℃×24 h | 发粘、鼓包、变色 | 低迁移油系 + 耐介质配方 |
文字版结论：九项里，界面三项（干态、湿热老化后、冷热循环后）必须一起看，只测干态等于没测；湿态摩擦系数是安全项，不能拿干态数据替代；压缩永久变形是这个件最容易被忽略的一项，因为它测的是"用久了还握得住吗"。把这张表当体检单，缺一项不判合格。
五、常见失效与根因：脱层、打滑、发粘、起泡，先查界面还是先查料
这个件上的早期失效，多数出在界面，不是出在软料本体。
失效一：延迟脱层——装起来看着粘住了，一周到一个月后整片松开。 根因通常是三条之一：软料充油量过高，小分子油迁移到界面形成隔离膜；硬芯表面残留脱模剂、手汗或抗氧化剂迁移层；以及假包胶，初期靠机械嵌合撑着，油膜一形成就分家。先查结合面的清洁与存放，再查配方，顺序反了会白试几轮。
失效二：湿手打滑。 这类投诉最容易被归到"硬度太高"，其实多半不是。据公开资料（B 级），干态摩擦系数一般要求在 0.5 以上（优质配方可达 0.8），真正的判据是沾水沾汗后的衰减率——控制在 15% 以内才算稳。干态好、湿态一塌糊涂的配方是存在的，所以必须干湿两态分开测。
失效三：软层长期被压薄、变硬、发亮。 根因是压缩永久变形没做够，按 GB/T 7759.1 测（压缩率 25%、70℃×22 h）。要纠正一个直觉：改善这一项靠回弹体系与软层厚度留量，不是把硬度调低——硬度低但回弹差的配方，用几个月照样塌。
失效四：玻纤外露区起泡剥离。 硬芯是 PP 加玻纤时，结合面露出的玻纤会削弱粘接，冷热循环的收缩差又在同一片区域叠加内应力——结合面尽量安排在没有浮纤的位置。
六、验证顺序：界面剥离为什么要做三次，而且排在摩擦系数之前
这一段同行几乎没人写，但这个件的钱就花在这上面。顺序错了，成本会在最后一步集中爆出来。
`
① 界面剥离（干态） 180° 剥离，看强度 + 破坏模式
↓ 低于 3 N/mm 或界面分离 → 退回，先别往下做
② 界面剥离（湿热老化后） 95℃×2 h 水煮后再测
↓ 衰减 >20% → 退回查充油量与接枝率
③ 界面剥离（冷热循环后） -40~85℃ 循环后再测
↓ 出现起泡 / 剥离 → 退回查浮纤与收缩差
④ 摩擦系数（干湿两态） 干态 μ、湿态衰减率
↓ 湿态衰减 >15% 或湿态 μ<0.5 → 退回改表面体系
⑤ 压缩永久变形与厚度保持 25% 压缩率、70℃×22 h
↓ 超门限 → 退回改回弹体系
⑥ 耐手汗与油脂 人工汗液、机油浸泡后复测
↓ 发粘 / 鼓包 / 变色 → 退回换低迁移油系
⑦ 跌落与整机装配 1.5 m 跌落无脱层、装配无干涉
↓
⑧ 握持体验 + 老化后复评
`
为什么界面要做三次、而且必须排在摩擦系数之前？因为界面是"能不能用"的门槛，摩擦系数是"好不好用"的门槛。 界面这一关不过，后面所有测试都是白做——手感调得再好，件在客户手里脱了层，一样是退货。第三次（冷热循环后）最容易被跳过：改性PP 硬芯与软层的收缩差会在转角累积应力，常温测不出来，循环几次就露头。
七、反向诚实：这四个条件同时出现，握住的地方就不该用 PP 基包胶
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 PP 基包胶不合适 | 该往哪走 |
|---|
| 要求长期 80℃ 以上 | SEBS 基软层与 PP 硬芯都接近耐温边界，油迁移加速、界面衰减变快 | 换极性硬芯 + 对应耐温配方，或走硅胶 / EPDM 硫化体系 |
| 要求极高耐磨 | SEBS 基 TPE 的耐磨不是强项，长期磨蚀后表面会先失光再起毛 | 走 TPU 包胶路线 |
| 界面要求绝对不脱（如高空作业、带电作业的安全手握位） | 粘接是概率事件，不能当安全冗余用 | 必须做机械锁扣或包边铆合，或回到结构方案（整体软芯 + 硬嵌件） |
| 软层极薄（<1 mm）同时要求高附着力 | 熔体来不及充分扩散，内聚强度不足，剥离曲线不稳定 | 换极性硬芯 + 极性配方；或改双色注塑（硬胶未冷却时直接包覆） |
规律是一致的：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 基包胶硬撑。 遇到这种情况，我们的做法是先把这条讲清楚，再谈有没有折中空间——硬接下来的单子，最后都要用返工和索赔还回去。
八、换料要动什么：包胶件的换料清单比单料件长一倍
包胶件换料，动的不是一个件，是两套料加一条界面。这张表建议先过一遍。
| 要动的项 | 需要确认什么 | 不做会怎样 |
|---|
| 模具与结构 | 结合面要不要做微凹槽、倒扣、贯穿孔；位置要避开熔接线 | 只靠粘接兜底，长期可靠性不可控 |
| 硬芯收缩率 | 硬芯收缩与外层收缩的差，决定转角与边缘的内应力 | 转角剥离、翘边 |
| 基材预处理与存放时效 | 结合面不得有脱模剂、油污、手汗；脱模到二次包胶的间隔越短越好 | 界面夹层，粘不住 |
| 料温与模温 | 硬芯料筒 180-220℃、模温 30-50℃；软料熔体温度比 PP 熔点高 15-25℃，且不宜超过 210℃ | 软料主链受损、界面发黄起泡 |
| 基材预热 | 预热 60-80℃；合模后注射前硬芯表面温度更高更稳 | 熔体一碰冷硬芯就凝，扩散层只有几纳米 |
| 干燥与排气 | 按具体体系定；软料体系对水分与排气敏感 | 银丝、气泡、界面缺陷 |
| 色差 | 品牌件必须先确认色板再上机 | 批次色差争议 |
| 验证顺序 | 界面剥离三次 → 摩擦系数 → 压缩永久变形 → 耐汗耐油 → 跌落装配 | 风险全部压到最后一步集中爆发 |
九、一页纸汇报对照表：软硬一体件怎么一次会定方向
| 场景 | 推荐路线 | 关键指标 | 验证标准 | 需先确认的条件 |
|---|
| 常规手动工具手柄（螺丝刀、扳手） | PP 硬芯 + SEBS 基 TPE（含 PP 组分） | 剥离 ≥3 N/mm 且本体撕裂；干态 μ ≥0.8 | GB/T 2790；ASTM D1894 | 硬芯牌号、是否长期皮肤接触 |
| 电动工具手柄（有振动与发热） | PP 硬芯 + 接枝型 SEBS 基 TPE，硬度 A45-55 | 湿态 μ 衰减 ≤15%；耐温 -40~90℃ | 摩擦系数干湿两态；80℃/24 h | 机身长时运行温度、法规要求 |
| 车间手柄（常沾机油、切削液） | 耐油体系，必要时 TPV 或 TPU | 介质浸泡后溶胀与强度变化 | 23℃×24 h 机油浸泡 + 剥离复测 | 介质种类与接触时长 |
| 长期皮肤接触 / 儿童或厨具柄 | 低迁移油系 + 合规配方 | 人工汗液色牢度、迁移量 | DIN 53160-2；食品接触按 GB 4806 | 目标市场与抽检标准 |
| 安全手握位（高空、带电） | 不靠粘接，走机械锁扣或改结构 | 结构冗余 | — | 是否在安全承力路径上 |
文字版结论：这张表的作用是让技术员把结论直接往上报。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、这个件上最容易出问题的，往往不是软料
公开的问题。 这类件最常见的早期失效是延迟脱层与湿手打滑，其中由软料本身引起的比例并不高。脱层多半落在三处：充油量过高导致油迁移、结合面残留脱模剂或手汗、以及只靠机械嵌合的假包胶。
公开的判据。 界面按 GB/T 2790（180° 剥离），门限 ≥3 N/mm 且破坏模式为软层本体撕裂；压缩永久变形按 GB/T 7759.1（压缩率 25%、70℃×22 h）；耐汗液按 DIN 53160-2 人工汗液色牢度；摩擦系数干湿两态分开测，湿态衰减 ≤15%。
行业通行的解法。 硬芯优先选共聚 PP 而非均聚（均聚结晶度高、表面能更低）；软料选 SEBS 基并配 PP-g-MAH 或 SEBS-g-MAH 做过渡层；结合面避开浮纤，做微凹槽与倒扣；基材预热并控制脱模到包胶的间隔。
我们常供什么。 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）粒子里的抗冲共聚方向，按所配的软层体系与件的收缩要求给到对应的基材档位与填充方案，主要用来解决上面说的"界面粘不牢、转角易剥离"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：软料的硬度做低一点，手感是不是就好了？
答：这是这个件上最容易走偏的一条。硬度只是手感的一个维度，另外三个维度至少同等重要——回弹速度（太快会"震手"，太慢会觉得"塌"）、表面摩擦系数（干手和湿手差别很大）、长期压缩后的厚度损失。只盯硬度，做出来的手柄很可能在湿手状态下打滑。行业上的常规范围是邵氏 A40-70，电动工具手柄常在 A45-55 之间，但那是起点，不是答案。
问：剥离强度我们自己打一次样就够了吗？
答：不够。要打三次——干态、湿热老化后、冷热循环后，而且三次都要看破坏模式。另有一个成本极低的自检办法：包胶件做撕扯测试时，撕开如果带出硬芯的丝、或者断在软层本体里，说明是粘住的；如果干净地从界面分开，那就是假包胶或界面已经有污染，数值再高也不可信。
问：客户要求长期皮肤接触，甚至要过食品接触，怎么办？
答：分两条线。长期皮肤接触看人工汗液色牢度（DIN 53160-2）与多环芳烃一类的限量要求，用低迁移油系；食品接触则要选食品级 SEBS 基与食品级白油，并按目标市场做迁移检测。这两件事要在选配方时就说清，不能等成型后再补报告。
问：硬芯是 PP 加玻纤，包胶老是起泡剥离，是不是料的问题？
答：先别换料，先查三处——结合面是不是有浮纤、是不是残留了脱模剂或手汗、脱模到二次包胶的间隔是不是拖得太久。这三处占的比例明显更高。料的问题一般表现为整批一致地脱；污染和浮纤表现为局部先起泡，两者的排查顺序不一样。
| 工况 | 关键判据 | 自产常规供应 |
|---|
| 手动工具手柄 | 剥离 ≥3 N/mm 且本体撕裂 | 抗冲共聚 PP 基材方向 + 收缩档配平 |
| 电动工具手柄 | 湿态摩擦衰减 ≤15%；耐温 -40~90℃ | 按耐温与收缩配填充档的抗冲共聚方向 |
| 车间手柄（沾油） | 介质浸泡后强度与溶胀 | 按介质给到对应的耐油适配方向 |
十一、最后说三句
第一句，包胶件的成败不在软料，在界面。 改性PP 硬芯的表面能只有 29-31 mN/m，界面这一关不过，手柄调得再舒服也是白调。
第二句，手感不能只用一个硬度去描述。 回弹速度、干湿两态的摩擦系数、长期压缩后的厚度损失，这三项和硬度同等重要；只调硬度，做出来的手柄很可能湿手打滑。
第三句，界面剥离要做三次。 干态、湿热老化后、冷热循环后，三次都过才算过；只测干态，等于把风险留到客户端。
关于我们
有些生意我们不做。
不问用途就报价的，不做。
把副牌料说成正牌卖的，不做。
承诺"什么工况都能用"的，不做。
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。
The tool handle is overmolded with modified PP. Success does not depend on the soft material, but on the interface. PP is a non-polar material with a surface energy of only 29-31 mN/m. In secondary injection molding, the soft layer must be directly overmolded on the hard core, and the interfacial adhesion is the first threshold. This article explains all at once the three interface methods, nine criteria, the verification sequence requiring three interface peel tests, and "the four conditions that, if they occur simultaneously, indicate that PP-based overmolding should not be used."
Regarding the handle rubber coating, the question customers ask most often is: 'If it's softer, will it feel better?'
I have seen a customer who makes power tools reduce the hardness of the handle's soft layer from Shore A65 to A45. It did feel softer to hold, but there were actually three more after-sales complaints: slipping when wet, edges of the overmold curling, and the soft layer becoming shiny and hard after being compressed for six months.
Conclusion first: The success or failure of overmolded parts does not lie in the soft material, but at the interface. For tool handle overmolding with modified PP, the first thing to solve is not the soft material, but the interface that is only a few microns thick.
Hardness is only one aspect of the feel; what truly determines how long this part can last is the adhesion at the interface and the soft layer's ability to maintain resilience under prolonged gripping pressure.
So the correct first sentence is: first ask whether it sticks or not, then ask whether it feels comfortable to grip or not. Below, we break it down into five layers: working conditions, interface, route, criteria, and verification.
1. Analysis of six working conditions: -40°C to 90°C, hand sweat and machine oil; the working conditions for coated parts and structural parts are not calculated using the same algorithm
The first load on a rubber-coated handle is 'compression,' not 'tension'; the first medium is hand sweat, not rainwater.
Looking at the six dimensions together:
| Dimension | Actual working conditions of the tool handle | Requirements for the materials |
|---|
| Temperature | Outdoor in winter - does not freeze at -40°C; electric tool body can run for a long time up to 90°C | Soft layer temperature resistance: -40~90℃; long-term use above 80℃ requires reevaluation |
| Load | Grip pressure (grip force can reach several hundred newtons, very small per instance); 1.5 m drop; continuous vibration from power tools | Rebound retention Impact resistance of interface Fatigue resistance |
| Medium | Hand sweat (including salt and lactic acid), engine oil and grease, cutting fluid, cleaning agents | Sweat-resistant, oil-resistant, does not swell or become sticky |
| Lifespan | The handle is an 'eight hours a day' part, not a 'used occasionally' part. | Thickness retention after long-term compression |
| Appearance and feel | Matte or textured surface; dry and wet friction coefficients; brand parts require color consistency | Wet anti-slip Color stability |
| Compliance | Flame retardant (for some electrical components), handheld power tool safety, long-term skin contact, food contact (kitchen utensil handles) | Flame Retardant Rating Migration and Colorfastness |
Among the six dimensions, only two have a veto nature: the interface and wet-state friction. Problems in the other dimensions at most result in a poor experience or rework; if these two have issues, one is unqualified, the other is a safety accident.
A professional detail: the holding pressure is actually very small, so small that ordinary compression tests are hardly even bothered to be done. But it is a continuous pressure for eight hours a day. To make the soft layer thinner, harder, and shinier, it’s not about a single strong force, but about time and frequency. So what really needs to be tested for this part is compression permanent deformation, not tensile strength.
2. The interface stage: The surface energy of PP is only 29-31 mN/m, three paths and their respective costs
PP is difficult to bond, and there is only one reason: it is a non-polar material with too low surface energy.
According to publicly available information (Class B), the critical surface tension of PP is about 29-31 dyn/cm, while most TPE systems are above 40 dyn/cm. The polarity of the two is mismatched, so when the molten soft material flows over the PP surface, it does not form molecular-level wetting. After cooling, a layer of micro-gaps remains at the interface—this is the source of the 'looks stuck, but peels off easily' phenomenon.
The industry calls this situation 'fake overmolding': it barely holds together through mechanical interlocking or van der Waals forces.
According to public information (Class B), a peel strength below 2 N/mm can basically be judged as fake coating; for genuinely adhered coated parts, the 180° peel strength should be above 3 N/mm. Moreover, the failure mode must be tearing of the soft layer itself, not interfacial separation. This point is even more important than the numerical value—it distinguishes between 'sticking' and 'hanging on'.
To make the interface really stick, there are three paths in the industry, each with different costs:
▸ Path One · Compatibilizer / Capacity-Enhancing Layer
The interface changes from physical entanglement to a chemical transition layer. According to publicly available information (Class B), adding 1-3% PP-g-MAH or 2-3% SEBS-g-MAH can increase the interfacial bonding strength from 0.8 MPa to above 1.5 MPa; when the grafting rate is controlled at 0.5%-1.5%, the interfacial strength can be increased by 50%-80%.
Cost ▸ One more step in the formulation work. Excess compatibilizer will reduce fluidity and increase cost, and it also needs to be balanced with the oil content—too much oil will migrate, which instead weakens the interface.
▸ Path Two · Mechanical Locking Structure
Achieve ▸ Rely on geometric interlocking as a fallback. Create micro-grooves on the mating surfaces (depth 0.15-0.3 mm, width 0.5-1 mm), chamfer the edges (30-45°, depth 0.5-1 mm), and make φ2-4 mm through holes for rivet locking. According to public data (Grade B), the peel force can be increased 2-3 times.
Cost ▸ The molds are complex; stress is concentrated at the holes and undercuts, which are high-risk points for subsequent cracking; the freedom of appearance is also limited.
▸ Path Three · Replace Hard Core Substrate
Once obtained ▸ directly switch to polar hard cores like PA, ABS, PC-ABS, with naturally easy-to-make interfaces, and increase the material temperature window to 190-230°C.
Cost ▸ Then that's not the material for this piece. The hard core no longer uses PP, so the position for the PP substrate on this part is useless. Honestly, this point cannot be glossed over just to make the plan look complete.
When it comes to the interface, soft materials solve half of it, and the hard core and structure solve the other half. Focusing only on adjusting the hardness with the soft material formula is underestimating the problem.
3. How to distinguish the three material routes: PP, SEBS, changing polarity of hard core, TPU/silicone/EPDM boundary
You don't need to argue about which route is better; just look at what the core material is, how much temperature resistance is needed, and how much oil and wear resistance is required.
| Route | Get what | Cost |
|---|
| PP hard core SEBS-based TPE (containing PP components / graft modified) | No primer needed, slip-resistant when wet, oil and sweat resistant, does not freeze or harden at -40℃, recyclable | The low surface energy interface of PP must be resolved first; there is an upper limit to long-term temperature resistance. |
| PP hard core pure SEBS-based TPE (without PP compatibility) | General-purpose, price-friendly | Peeling force is only 0.3-0.8 N/mm, belonging to the pseudo-encapsulation range |
| Changing polarity of hard core (PA / ABS / PC-ABS) Polar formulation TPE | The interface is naturally easy to make, and the material temperature window is 190-230°C | The core material has been changed, and the cost, moisture absorption, and dimensions follow along. |
| TPU Coating | Outstanding wear and oil resistance | Primarily based on polar substrates; feels relatively hard, harder at low temperatures |
| Silicone overmolding | Skin-friendly, good temperature and weather resistance | Does not chemically bond with PP, requires primer or mechanical structure; high cost |
| EPDM vulcanized coated rubber | Good weather resistance and temperature resistance, low raw material cost | Relies on vulcanization molding, with a long cycle; does not primarily bond chemically with PP |
Here we need to clarify a set of concepts that are easily confused: 'TPE and PP' is not a single material, but a category of materials.
Pure SEBS-based TPE has only weak interaction with PP, with a typical peel strength of 0.3-0.8 N/mm; if a certain proportion of PP resin is pre-added to the SEBS matrix, the PP component and hard-core PP undergo co-crystallization during melting, increasing the peel strength to 2.5-4.0 N/mm; further grafting maleic anhydride onto the molecular chain (grafting rate 0.5%-1.5%) achieves bonding through chemical bonds, reaching 3.5-5.5 N/mm.
The difference lies in 'whether there is a segment co-crystallized with PP', not in how soft it is. Many customers bring a material labeled 'for PP only' and ask why it still falls off. The answer is often that this particular material is only made for general compatibility and does not have co-crystallization or grafting.
The three approaches are for division of labor, not substitution: for a soft layer that needs to be extremely wear-resistant, look at TPU; for temperature and weather resistance, consider silicone or EPDM; if you need no primer, wet-state slip resistance, and recyclability, go with SEBS-based TPE over PP. Using modified PP for a hard core and SEBS-based TPE for the soft layer is a relatively smooth combination in terms of cost and process, provided that the interface issue is resolved first.
Dare to challenge a common practice: when the feel is rough, people add lubricants to the soft material (like erucamide or oleamide). This is wrong, and the mistake is very subtle. These additives continuously migrate to the surface, forming a separating layer at the bonding interface, which exactly destroys the interfacial strength. The slight slipperiness you add to improve the feel is actually the starting point of delamination. To improve the feel, what needs to be adjusted is the surface texture and the hardness-thickness combination, not adding migrating additives.
4. ★ Selection Criteria Table: How to Test Nine Items from Interface Separation to Wet Friction Coefficient
The table below is the part of the entire article that should be collected the most, arranged according to the combination of modified PP hard core and soft layer coating. Pay attention to the third column 'Verification Method'—for this component, the most common point of confusion is not 'which indicator to look at,' but 'what to use for measurement, what measurement result counts as passing, and what the appearance of damage looks like to be considered qualified.'
| Indicator | Threshold (typical) | Verification Method / Standard | Common Failures | Common solution |
|---|
| 180° Peeling Strength (Dry State) | ≥3.0 N/mm, and the failure mode is tearing of the soft layer itself | GB/T 2790 / ISO 8510-1 / ASTM D903 | Interface peeling, edge curling | Compatibilizer Substrate Preheating Anchoring Structure |
| Peel Strength (after damp heat aging) | After boiling at 95℃ for 2 hours, the degradation is ≤20% | GB/T 2790 Boiling Pretreatment | Delayed delamination | Low-migration oil-based High-graft compatibilizer |
| Peel strength (after hot and cold cycles) | No visible bubbling or peeling after cycling | GB/T 2790 -40~85℃ Cycle | Foaming in the floating fiber area and corner delamination | Avoid floating fibers Replenish polar components |
| dry friction coefficient | μ ≥ 0.8 (more lenient standard ≥ 0.5) | ASTM D1894 / GB/T 10006 (specify the friction surface) | Can't hold, slippery | Surface texture Adjust formula for friction |
| Friction coefficient in wet condition (hand sweat/water) | Attenuation ≤15%, wet state μ still > 0.5 | Same as above; moistened with artificial sweat or water | Slippery when wet | Wet anti-slip system |
| Shore Hardness A | 40-70 (common for power tool handles: 45-55) | GB/T 531.1 / ISO 7619-1, 23±2℃ | Difficult to exert force or fatigued after holding for a long time | Coordination of hardness and thickness |
| Compression set | Compression ratio 25%, evaluated according to the item standard after 70°C × 22 h | GB/T 7759.1 / ISO 815-1 / ASTM D395 | Soft layer thinning, grip strength decreasing | Rebound system Thickness allowance |
| Tear strength | ≥15 kN/m | GB/T 529 / ISO 34-1 | Split flange | Matching of body strength and hardness |
| Resistant to sweat and oil | The color difference and mechanical changes after soaking in artificial sweat/lubricating oil are within the threshold | DIN 53160-2 (artificial sweat, pH 6.5); medium soaking 23°C × 24 h | Sticky, bulging, discolored | Low-migration oil-based medium-resistant formula |
Text Version Conclusion: Among the nine items, the three interface items (dry state, after humid heat aging, after thermal cycling) must be considered together; measuring only the dry state is equivalent to not measuring at all. The friction coefficient in the wet state is a safety factor and cannot be replaced with dry state data. Permanent compression deformation is the item most easily overlooked for this part, because it measures whether it can still be held after prolonged use. Treat this table like a medical check-up sheet; if any item is missing, it is not considered qualified.
5. Common Failures and Root Causes: Delamination, slipping, stickiness, bubbling—should we check the interface first or the material first?
The early failures of this part mostly occur at the interface, not in the soft material itself.
Failure 1: Delamination Delay — At first, it looks stuck together, but after a week to a month, the whole piece comes apart. The root cause is usually one of three things: too much oil in the soft material, with small molecule oil migrating to the interface and forming a separating film; residual mold release agent on the hard core surface, sweat, or migration layer of antioxidants; or false overmolding, initially held together by mechanical fit, which separates once the oil film forms. First check the cleanliness and storage of the bonded surface, then check the formulation — if you do it in the reverse order, you'll waste a few rounds of testing.
Failure Two: Slipping with wet hands. Complaints of this type are most easily attributed to "too high hardness," but this is often not the case. According to publicly available data (B level), the coefficient of friction in a dry state generally needs to be above 0.5 (high-quality formulations can reach 0.8). The real criterion is the decay rate after contact with water or sweat—maintaining it within 15% is considered stable. Formulations that perform well when dry but poorly when wet do exist, so it is necessary to test separately under both dry and wet conditions.
Failure 3: The soft layer becomes thin, hard, and shiny over a long period of compression. The root cause is insufficient permanent deformation under compression, tested according to GB/T 7759.1 (compression rate 25%, 70°C × 22 h). One intuition to correct: improving this relies on the resilience system and the reserved thickness of the soft layer, not by lowering the hardness—formulas with low hardness but poor resilience will still collapse after a few months.
Failure Four: Bubbling and peeling in exposed fiberglass areas. When the hard core is PP with fiberglass, the exposed fiberglass at the bonding interface can weaken adhesion, and the shrinkage differences from thermal cycling add internal stress in the same area—therefore, the bonding interface should be arranged where there are no floating fibers.
6. Verification sequence: Why is interface debonding done three times, and why is it performed before the friction coefficient
Almost no one in the industry writes this part, but the money for this piece is all spent on it. If the order is wrong, the costs will all come out at the final step.
`
① Interface Delamination (Dry State) 180° peeling, check strength Failure mode
↓ Less than 3 N/mm or interface separation → Return, do not proceed further for now
② Interface delamination (after damp heat aging) Boil at 95℃ for 2 hours before testing again
↓ Attenuation >20% → Return to check oil filling amount and grafting rate
③ Interface delamination (after hot and cold cycling) - Measure again after cycling from -40 to 85℃
↓ Bubbling / Peeling → Return to check floating fibers and shrinkage difference
④ Coefficient of friction (dry and wet states) Dry state μ, wet state decay rate
↓ Wet state degradation >15% or wet state μ <0.5 → return to modify the surface system
⑤ Compressive permanent deformation and thickness retention: 25% compression, 70°C × 22 h
↓ Exceed Threshold → Return to Correct Rebound System
⑥ Resistance to hand sweat and oil Retested after soaking in artificial sweat and machine oil
↓ Sticky / Bubbling / Discoloration → Return and replace with low migration oil system
⑦ Drop and Complete Machine Assembly No delamination after 1.5 m drop, no interference in assembly
↓
⑧ Grip experience Re-evaluation after aging
`
Why does the interface need to be done three times, and why must it come before the friction coefficient? Because the interface is the threshold of "whether it can be used," while the friction coefficient is the threshold of "whether it is good to use." If the interface fails, all subsequent tests are useless—no matter how good the feel is, if the parts delaminate in the customer's hands, they will be returned. The third time (after thermal cycling) is the easiest to skip: the shrinkage difference between the hard core and soft layer of modified PP will accumulate stress at the corners, which cannot be detected at room temperature, but will appear after a few cycles.
7. Reverse honesty: When these four conditions appear simultaneously, the places being held should not use PP base wrapping
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 PP base coating is not suitable | Which way should I go? |
|---|
| Requires long-term exposure above 80℃ | The SEBS soft layer and PP hard core are both close to the temperature tolerance limit, causing faster oil migration and quicker interface degradation. | Change to polar hard core corresponding to heat-resistant formulation, or use silicone/EPDM vulcanization system |
| Requires extremely high wear resistance | SEBS-based TPE does not have strong wear resistance; after long-term abrasion, the surface will first lose its gloss and then become fuzzy. | Take the TPU coating route |
| The interface must absolutely not slip (such as safe hand-hold positions for high-altitude work or live electrical work) | Adhesion is a probabilistic event and cannot be used as a safety redundancy. | It is necessary to use mechanical locks or edge riveting, or return to the structural scheme (overall soft core with hard inserts). |
| The soft layer is extremely thin (<1 mm) while also requiring high adhesion | The melt does not have enough time to fully diffuse, the cohesive strength is insufficient, and the peel curve is unstable | Change to a polar hard core; polar formulation; or switch to two-color injection molding (directly encapsulate the hard plastic before it cools) |
The pattern is consistent: whenever there are 'two conflicting requirements at the same time,' it indicates that PP basic encapsulation should not be used for this part. In such cases, our approach is to first clarify this point, and then discuss whether there is room for compromise—orders that are forcibly accepted will ultimately have to be reworked and returned for compensation.
8. What needs to be moved when changing materials: The material change list for overmolded parts is twice as long as that for single-material parts.
For replacing the encapsulated parts, it's not just one part being moved, but two sets of materials plus one interface. It's recommended to go through this table first.
| Items to move | What needs to be confirmed | What will happen if I don't do it? |
|---|
| Mold and structure | Whether to make micro-grooves, undercuts, or through holes at the mating surface; the position should avoid weld lines | Relying solely on bonding for coverage makes long-term reliability uncontrollable |
| Core shrinkage rate | The difference between core shrinkage and outer layer shrinkage determines the internal stress at corners and edges | Corner peeling, edge lifting |
| Substrate Pretreatment and Storage Aging | The bonding surface must be free of release agent, oil, and hand sweat; the shorter the interval between demolding and secondary encapsulation, the better. | Interface layer, cannot stick |
| Material Temperature and Mold Temperature | Hard core material barrel: 180-220℃, mold temperature: 30-50℃; soft material melt temperature is 15-25℃ higher than the PP melting point, and should not exceed 210℃ | Damage to the soft material main chain, interface yellowing and blistering |
| Substrate Preheating | Preheat to 60-80°C; after closing the mold, the surface temperature of the hard core is higher and more stable before injection | The melt solidifies as soon as it touches the cold hard core, and the diffusion layer is only a few nanometers thick. |
| Drying and Venting | Determined according to the specific system; soft material systems are sensitive to moisture and venting | Silver threads, bubbles, interface defects |
| Color difference | Branded parts must confirm the color swatch before production | Batch color difference dispute |
| Verification order | Interface delamination three times → friction coefficient → compression set → sweat and oil resistance → drop assembly | All the risks are concentrated to explode at the final step |
9. One-page report comparison table: How to set the direction of an integrated soft and hard component in one go
| Scene | Recommended Route | Key indicators | Verification Standard | Conditions that need to be confirmed first |
|---|
| Conventional manual tool handles (screwdrivers, wrenches) | PP hard-core SEBS-based TPE (contains PP components) | Peel ≥3 N/mm and body tear; dry state μ ≥0.8 | GB/T 2790; ASTM D1894 | Hard core grade, whether it is in long-term skin contact |
| Electric tool handle (with vibration and heating) | PP hard-core grafted SEBS-based TPE, hardness A45-55 | Wet-state μ attenuation ≤15%; temperature resistance -40~90℃ | Friction coefficient in dry and wet states; 80°C/24 h | Operating temperature of the airframe for long durations, regulatory requirements |
| Workshop handles (often covered with machine oil and cutting fluid) | Oil-resistant system, TPV or TPU if necessary | Swelling and strength changes after medium immersion | 23℃ × 24 h oil immersion Delamination retest | Type of medium and duration of contact |
| Long-term skin contact / children or utensil handles | Low migration oil-based compliant formulation | Color fastness and migration of artificial sweat | DIN 53160-2; food contact according to GB 4806 | Target Market and Sampling Standards |
| Safe hand grip position (high altitude, live electricity) | Do not rely on bonding; use mechanical locks or modify the structure | Structural redundancy | — | Is it on the safe load-bearing path? |
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 part that is most prone to problems on this item is often not the flexible material.
Public issues. The most common early failures of this type of part are delayed delamination and slipping when handled with wet hands, and the proportion caused by the soft material itself is not high. Delamination mostly occurs in three areas: excessive oil filling leading to oil migration, release agent or hand sweat residue on the bonding surface, and pseudo overmolding that relies solely on mechanical interlocking.
Public criteria. The interface is tested according to GB/T 2790 (180° peel), with a threshold ≥3 N/mm and a failure mode of substrate tearing of the soft layer; permanent compression deformation is tested according to GB/T 7759.1 (compression ratio 25%, 70°C × 22 h); sweat resistance is tested according to DIN 53160-2 using artificial sweat for color fastness; the coefficient of friction is measured separately for dry and wet states, with wet state attenuation ≤15%.
Industry-standard solutions. For hard cores, preferentially choose copolymer PP rather than homopolymer (homopolymer has higher crystallinity and lower surface energy); for soft materials, use SEBS-based material combined with PP-g-MAH or SEBS-g-MAH as a transition layer; avoid floating fibers at the bonding interface, and create micro-grooves and undercuts; preheat the substrate and control the interval from demolding to overmolding.
What we commonly supply. Ningbo Kolon New Materials Co., Ltd. commonly supplies in this area are impact-resistant copolymer-oriented modified polypropylene (PP) particles. According to the soft layer system used and the part's shrinkage requirements, we provide the corresponding substrate grades and filling schemes, mainly to address the two issues mentioned above: 'poor interface adhesion and easy peeling at corners.' The formulation is adjusted according to the operating conditions of the part and can be used to make small sample comparisons and mold trials. We can also meet the needs of part-level customers for multiple varieties in small batches.
Frequently Asked Questions
Question: If the hardness of the soft material is reduced, will the feel be better?
Answer: This is the aspect most prone to deviation in this component. Hardness is only one dimension of the feel; the other three dimensions are at least equally important — rebound speed (too fast will cause a 'shock,' too slow will feel 'sinking'), surface friction coefficient (which varies greatly between dry and wet hands), and thickness loss after long-term compression. Focusing only on hardness, the resulting handle is likely to slip when hands are wet. The conventional industry range is Shore A40-70, with power tool handles often between A45-55, but that is just a starting point, not the answer.
Question: Is it enough for us to make just one sample for peel strength?
Answer: Not enough. It needs to be tested three times—after dry conditions, after damp heat aging, and after thermal cycling, and the failure mode must be examined each time. There is also a very low-cost self-check method: during a tear test on the coated parts, if tearing brings out fibers from the hard core, or breaks within the soft layer itself, it indicates bonding; if it cleanly separates at the interface, it is a false coating or the interface is already contaminated, and even high values are not reliable.
Question: The customer requires long-term skin contact, or even food contact. What should we do?
Answer: There are two approaches. For long-term skin contact, check the color fastness to artificial sweat (DIN 53160-2) and the limit requirements for polycyclic aromatic hydrocarbons, using low-migration oil-based materials; for food contact, you need to choose food-grade SEBS and food-grade white oil, and conduct migration testing according to the target market. These two things need to be clarified when selecting the formulation, and you can't add the report after molding.
Q: The hard core is PP with glass fiber, but the rubber coating keeps bubbling and peeling. Is it a material problem?
Answer: Don’t change the material yet. First, check three places — whether there are floating fibers on the joint surface, whether there is leftover mold release agent or hand sweat, and whether the interval between demolding and secondary coating is too long. These three factors have a significantly higher proportion of cases. Problems with the material generally show as consistent detachment across the whole batch; contamination and floating fibers show as localized bubbling first, and the order of checking these two is different.
| Operating condition | Key criterion | Self-produced regular supply |
|---|
| Hand tool handle | Peeling ≥3 N/mm and substrate tearing | Impact Copolymer PP Substrate Orientation Shrinkage Range Matching |
| Electric tool handle | Wet friction decay ≤15%; temperature resistance -40~90℃ | Direction of impact-resistant copolymer filling according to temperature control and shrinkage match |
| Workshop handle (oily) | Strength and swelling after medium immersion | Provide the corresponding oil-resistant adaptation direction according to the medium |
Eleven, finally say three sentences
The first sentence: the success or failure of overmolded parts does not lie in the soft material, but at the interface. The surface energy of a modified PP hard core is only 29-31 mN/m. If the interface fails, no matter how comfortable the handle is adjusted, it is all in vain.
The second point is that feel cannot be described by hardness alone. Rebound speed, friction coefficients in both dry and wet states, and thickness loss after long-term compression are equally important as hardness; if you only adjust hardness, the handle made may easily slip when wet.
The third sentence: interface delamination must be done three times. It is only considered passed if it passes all three tests: in the dry state, after damp heat aging, and after thermal cycling; testing only in the dry state is equivalent to leaving the risk to the client.
About Us
There are some businesses we don't do.
We don't provide quotes without asking about the purpose.
Selling secondary-grade materials as the main brand will not be done.
I won't do it if it 'promises' to work under any conditions.
Ningbo Cologne New Materials Co., Ltd. produces modified polypropylene (PP) granules, covering homopolymer, random copolymer, and block copolymer base materials, as well as modifications including filled, glass fiber reinforced, toughened, flame-retardant, low odor and low VOC, weather-resistant, and scratch-resistant without coating; it also deals in PP resins from major petrochemical plants, off-spec materials, and bulk materials.
