冰箱内胆用改性PP、洗衣机内桶用改性PP，但这两个件怕的东西完全不一样：内胆怕背面聚氨酯发泡层里的发泡剂渗透进来诱发开裂鼓包，内桶怕高速脱水的循环疲劳叠加洗涤剂 ESC。这篇把两个件的工况六维、判据、验证顺序与反向诚实分开讲。
"料没变，配方没动，冰箱用了半年，内胆拐角自己裂了。"
一个做冷柜的技术员这么跟我说。不是撞的，是慢慢鼓起一道细纹，顺着拐角走，越扩越长。
另一个做洗衣机的工程师说：内桶脱水转速提上去之后，跑了若干个周期，桶壁出现径向细纹，固定螺丝也松了。
两个件都用改性PP，失效现场看着都像"脆了"，根子却不是一个方向。把这两个件当成同一种"PP 件"来选料，是家电选材里最常见的错法。
一、冰箱内胆与洗衣机内桶都用改性PP，怕的东西却不是一个方向
结论先说：这两个件的失效归因完全不同——内胆多是发泡层那一侧的渗透，内桶多是疲劳与洗涤剂共同作用。
内胆出问题，多半不是冲击韧性不够，是发泡剂从背面慢慢渗进来诱发的；内桶出问题，多半不是一下撞碎，是几千次脱水循环加洗涤剂泡着磨开的。
所以下面不混着讲，两个件各拆一套工况、各走一套验证。这道"先分边"的判断，比任何配方建议都值钱——它直接决定你该先查发泡料，还是先查转速与循环次数。
二、冰箱内胆工况六维：发泡层相容性是这一件的分水岭
结论先说：六维里"介质"这一维才是内胆的分水岭，而这个介质不是清洁剂，是背面那层聚氨酯发泡料。
| 维度 | 内胆的实际工况 | 对材料的要求 |
|---|
| 温度 | 冷藏 0~4℃、冷冻 −18℃ 一级；开门时从室温骤降到腔温 | 低温保持韧性，不开裂 |
| 载荷 | 发泡层膨胀给的背压 + 内胆自重 + 食物载荷 | 刚性够、不变形即可 |
| 介质 | 聚氨酯发泡层里的发泡剂（环戊烷类、LBA 类）长期从背面渗透；油脂与食物汁液；清洁剂擦拭 | 耐发泡剂迁移（最贵的一维）；耐油、耐清洁剂 |
| 寿命 | 整机常按 10-15 年设计 | 长期不裂、不鼓包、不脆化 |
| 外观 | 平整光洁、易清洁；PP 件吸附气味后难去除 | 低气味、易清洁、表面无缩陷 |
| 合规 | 直接接触食物 → GB 4806.7-2023；抗菌防霉另有家电件口径 | 总迁移等限值达标；必要时抗菌 |
文字版结论：温度不是最难的，介质才是。 "胆裂、鼓包"的机理是：发泡剂小分子（环戊烷类蒸气最典型）被 PP 基体吸收 → 增塑溶胀、玻璃化温度下降、局部生成微泡 → 在残余应力下诱发环境应力开裂。选型第一句该问"发泡层什么体系、密度多少、工艺温度区间"。
一个内行细节：内胆大多是热成型（吸塑）件，残余内应力比注塑件更难释放，壁厚不均又让薄处应力更集中。同一包料，注塑件没事、吸塑内胆却裂，常常是成型内应力没压住。
公开口径里，影响渗透开裂的主要是四个因素：内胆壁厚、成型内应力、材料结晶度、发泡料密度与工艺窗口。对策三条一起上：选耐发泡剂牌号、控成型内应力（片材温度、拉伸比、必要时退火）、结构上避开尖角与过薄区。内胆这一侧，材料不是第二道——发泡剂与基体的相容性本身就是"介质"这一维的直接答案。
三、洗衣机内桶工况六维：高速脱水疲劳与洗涤剂是双主因
结论先说：内桶的分水岭是"循环疲劳 + 洗涤剂"——它不是被一下撞坏的，是被几千次脱水循环和表面活性剂共同磨开的。
| 维度 | 内桶的实际工况 | 对材料的要求 |
|---|
| 温度 | 常温到高温洗涤（部分程序 60-90℃），漂洗骤降 | 耐温冲、长期不变形 |
| 载荷 | 高速脱水离心载荷，转速越高离心力越大；不平衡是常态，动平衡失衡会放大局部载荷 | 抗长期循环疲劳、动平衡稳 |
| 介质 | 洗涤剂 + 柔顺剂长期接触（表面活性剂），漂洗后仍有残留 | 耐洗涤剂 ESC |
| 寿命 | 按脱水循环次数设计（常用数千到上万次一级） | 按循环次数验，不按单次极限 |
| 外观 | 耐污、易清洁、不挂污 | 表面光洁、抗菌防霉 |
| 合规 | 处在潮湿水系统；抗菌防霉常用 | 防霉等级；洗衣机件按家电抗菌口径 |
文字版结论：载荷这一维是循环疲劳，不是静态强度。 转速越高、离心载荷越大，长期循环后可能变形、开裂、紧固点松动。看单次冲击值看不出问题，必须上循环台架、按次数记结果。
一个内行细节：内桶是注塑件，常按 MFR 20-40 g/10min（GB/T 3682 口径）选料。它的内应力来自浇口、保压与筋位；更致命的是动平衡——桶体一点偏心，脱水时系统共振，疲劳寿命直接打折。内桶的"料"，要和"结构 + 动平衡"一起看。
四、材料路线分工：抗冲共聚PP、增韧改性PP、ABS/HIPS、不锈钢内桶各管一段
结论先说：这四条路线不是替代关系，是分工关系——抗冲共聚 PP 接内胆的低温与吸塑，增韧改性 PP 接内桶的韧性与耐洗涤剂，ABS/HIPS 接表面与尺寸，不锈钢内桶接耐久。
| 路线 | 拿到什么 | 代价 | 适合哪一段 |
|---|
| 抗冲共聚 PP（内胆主力） | 耐低温、易挤板吸塑、食品接触可行 | 耐发泡剂要专门体系；普通抗冲共聚挡不住环戊烷类渗透 | 冰箱内胆、抽屉、果蔬盒 |
| 增韧改性 PP（内桶主力） | 韧性高、耐洗涤剂 ESC、可注塑复杂筋位 | 疲劳寿命要靠壁厚与结构补；加矿物或玻纤后表面变粗 | 洗衣机内桶、波轮、外桶 |
| ABS / HIPS（内胆常见替代） | 表面好、易成型、尺寸稳 | 耐温一般；与 PU 发泡层粘结要另做处理 | 对外观与尺寸要求高的内胆段 |
| 不锈钢内桶 | 耐疲劳、耐腐蚀 | 成本高、重量大，不属 PP 体系 | 高负载内桶、商用机型 |
文字版结论：PP 系接"轻、成本方向低、耐化学、易成型"；ABS/HIPS 接"表面与尺寸"；不锈钢接"耐久"。 同一台冰箱或洗衣机上几种料各管一段是常态。选型只做分工陈述，不给"谁更好"的结论。
边界要说清：内胆若长期贴强极性发泡体系，材料体系比增韧量更关键；内桶若追求高转速长寿命，PP 的疲劳上限会先到，要靠壁厚、加强筋、动平衡与紧固设计补。
五、★ 选型判据表：内胆与内桶分开列，每项都带验证方法
结论先说：这张表的价值在第三列——卡住你的通常不是"该看哪一项"，是"拿什么测、测到多少算过"。
| 指标 | 门限值（典型） | 验证方法 · 标准号 | 常见失效 | 通行解法 |
|---|
| 【内胆】耐发泡剂相容（带应力） | 带应力试样在实际发泡剂环境下不开裂、不鼓包 | 按实际发泡体系自定介质的带应力浸泡；应力加载可借 ASTM D1693、ISO 6252、ISO 22088-3 的思路 | 拐角细纹、鼓包、胆裂 | 耐发泡剂体系 + 控成型内应力 + 避尖角过薄 |
| 【内胆】低温冲击 | 按件定：−20~−30℃ 保持韧性 | GB/T 1843（悬臂梁，等同 ISO 180 体系） | 冷冻与开门温差脆裂 | 抗冲共聚 + 增韧体系 |
| 【内胆】食品接触 | 总迁移 ≤10 mg/dm²、高锰酸钾消耗 ≤10 mg/kg、重金属（以 Pb 计）≤1 mg/kg、脱色阴性；含芳香族异氰酸酯或偶氮着色剂的另需芳香族伯胺迁移总量不得检出（检出限 0.01 mg/kg） | GB 4806.7-2023（方法 GB 31604.8 / .2 / .9 / .52） | 合规不达标 | 食品级全新料 + 控低分子析出 |
| 【内胆】气味与抗菌防霉 | 低气味、抗菌活性与防霉等级按件定 | 抗菌 ISO 22196:2011 / GB/T 31402-2015 贴膜法（24 h）；防霉 ISO 16869:2008 / ASTM G21（28℃、14 天）；家电件另有 GB 21551.4-2010 | 异味吸附、霉斑 | 低气味体系 + 银离子/锌系抗菌剂 |
| 【内桶】耐洗涤剂 ESC（带应力） | 带应力试样在洗涤剂中到目标时长不开裂 | 弯条法 ASTM D1693（10% Igepal CO-630、50±0.5℃ 记 F₅₀）；恒拉伸应力法 ISO 6252 | 桶壁径向细纹 | 耐洗涤剂稳定体系 |
| 【内桶】脱水循环疲劳 | 按循环次数：径向变形、裂纹、紧固点松动不超限 | 脱水循环台架（按脱水转速与循环次数） | 径向裂纹、紧固松动、失圆 | 壁厚 + 加强筋 + 动平衡 + 紧固设计 |
| 【内桶】耐温与尺寸 | 长期耐温不变形；收缩率与外壳间隙、与波轮/滚筒配合达标 | GB/T 1634（负荷变形温度）；GB/T 17037.4 / ISO 294-4 | 高温失圆；装配偏、间隙超差 | 增强体系控 HDT + 矿物填充控收缩，先看浇口 |
文字版结论：最该先做的是第一行和第五行，两行都必须带应力试样。 拉伸、冲击、收缩都有现成报告，介质浸泡要自定介质、应力与时间——前面全过、这一关不过，整批方案作废。
内桶另有一组件级参考口径：MFR 20-40 g/10min（GB/T 3682 口径）、23℃ 缺口冲击 >6 kJ/m²、−20℃ >3 kJ/m²、弯曲模量 >1667 MPa。介质侧有公开量级锚点：有商用抗冲共聚牌号在 10% Igepal、50℃ 下记录到 500 h 以上未开裂——是锚点，不是门限。判据写成三要素：温度 + 时长 + 结果。
六、常见失效与根因：内胆多从发泡侧起裂，内桶多从疲劳与洗涤剂起裂
结论先说：这两个件的归因完全不同，混为一谈就是选料反复返工的根源。
失效一：内胆拐角细纹、鼓包。 根因多半不是"料太脆"，是发泡剂从背面渗透、起增塑溶胀，在残余应力下起裂。敢否定一个常见做法：把它归为"料不够韧、加增韧剂"是错的。 增韧解决不了小分子渗透——要动的是耐发泡剂体系，同时压低吸塑成型内应力、结构上避开尖角与过薄区。
失效二：内桶径向细纹、紧固点松动。 根因是循环疲劳叠加洗涤剂 ESC。同样敢否定一个常见做法：只看单次冲击值判断内桶料，是看不出来的。 必须按脱水循环次数上台架，看几千次之后的变形、裂纹与紧固保持力。
失效三：内胆异味、内桶霉斑。 前者是 PP 件吸附气味后难去除，后者是内桶长期潮湿、防霉等级不够，都靠低气味体系加减菌/防霉方案，按 ISO 22196 / ISO 16869 验证。
一条新判断。 不少讲开裂的文章把"降内应力、改结构"直接当成第一道解。这两个件上，前面还有一步更关键：先分清是哪一侧的因——内胆的因多在发泡层那一侧，内桶的因多在疲劳与洗涤剂的共同作用。先分边，再换料；顺序反了，换几轮还在原地。
七、验证顺序：冰箱内胆与洗衣机内桶是两套流程
结论先说：只有一条原则——把最可能一票否决、也最容易漏做的那一关放在最前面；两个件的最前一关不是同一关。
冰箱内胆验证顺序（发泡剂相容一票否决）：
`
① 发泡剂相容（带应力） 按实际发泡体系定介质；带应力试样；记"开裂／未开裂 + 鼓包 + 外观变化"
↓ 不过，后面不用做；退回耐发泡剂体系 + 成型内应力与结构
② 低温冲击 −20~−30℃ 缺口冲击，试样状态按 GB/T 1843
↓ 不过，退回抗冲共聚档位与增韧量
③ 热成型后内应力与尺寸 残余应力、壁厚分布、收缩与装配间隙
↓ 不过，退回成型工艺（片材温度／拉伸比／退火）与壁厚设计
④ 气味与抗菌防霉 低气味验收 + 抗菌 ISO 22196 / 防霉 ISO 16869
↓ 不过，退回低气味体系与抗菌剂方案
⑤ 整机发泡验证 装机后走真实发泡，观察内胆与发泡层界面
↓ 不达标，回到①重排体系
`
洗衣机内桶验证顺序（洗涤剂 ESC 一票否决）：
`
① 洗涤剂 ESC（带应力） 按实际洗涤剂定介质；弯条法 ASTM D1693 / 恒拉伸应力法 ISO 6252
↓ 不过，后面不用做；退回耐洗涤剂体系
② 脱水循环疲劳 按脱水转速与循环次数上台架；测径向变形、裂纹、紧固保持力
↓ 不过，退回壁厚／加强筋／动平衡／紧固设计
③ 高温与温冲 高温洗涤程序 + 漂洗温降循环，测变形与失圆
↓ 不过，退回增强体系与耐温档位
④ 尺寸与装配 收缩率、与外壳间隙、与波轮／滚筒配合
↓ 不过，退回填充量与浇口位置
⑤ 整机运行验证 整机洗涤 + 脱水循环，长期观察
`
文字版结论：内胆最容易漏①（发泡剂相容），内桶最容易漏①（洗涤剂 ESC），两关都要带应力试样。 最常见的错法是拿无应力试样泡介质——泡很久没事，带应力一周就裂，等于把开裂留到装机半年后。
八、反向诚实：这三种情况，这个件不该用改性PP
结论先说：只要出现"强极性介质长期接触且不许开裂"或"高透明"这类要求并存，就说明这个件不该用改性PP 硬撑。
| 出现的情况 | 为什么改性PP不合适 | 该往哪走 |
|---|
| 内胆长期贴强极性发泡体系，且要求绝不开裂鼓包 | 普通抗冲共聚即便增韧加满，也难挡住发泡剂小分子长期渗透 | 走相容性已验证的专用复合料；或加隔离层、改金属内胆方案 |
| 洗衣机内桶要求长期高温 + 高强度脱水（商用、工业级高转速高负载） | PP 的耐温与疲劳寿命有上限，循环次数与离心载荷到顶后径向裂纹难控 | 走不锈钢内桶，或玻纤增强工程塑料内桶 |
| 内胆要求高透明（展示柜、看食物用途） | PP 半透，透明牌号雾度也有限 | 走透明 PETG／PC 或玻璃内胆 |
文字版结论：不是改性PP 做不到某一项，是做不到"强极性发泡长期接触 + 绝不开裂"或"高透明 + PP"这类方向相反的两项同时满配。 硬接下来的单子，最后都要用返工和索赔还回去。
九、换料风险清单：吸塑内胆与注塑内桶要确认的事不一样
结论先说：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"——内胆是吸塑、内桶是注塑，要确认的项不完全一样。
| 要动的项 | 内胆（吸塑）要确认 | 内桶（注塑）要确认 | 不做会怎样 |
|---|
| 成型收缩率 | 吸塑拉伸比与回弹、壁厚分布 | 注塑收缩率与长件尺寸，GB/T 17037.4 | 尺寸超差、装配对不上 |
| 模具与排气 | 吸塑模表面与气路 | 浇口位置、排气（外观件更敏感） | 充填不足、熔接线弱 |
| 料温与模温 | 片材温度与吸塑模温窗口 | 料温／模温与停留时间 | 分解、内应力偏高 |
| 干燥 | 按具体体系定 | 按具体体系定 | 银丝、气泡 |
| 保压与脱模 | 退火降残余应力 | 保压决定内应力，顶出防拉伤 | 内应力偏高，抬高开裂风险 |
| 色差 | 浅色内胆先定色板 | 浅色内桶先定色板 | 批次色差争议 |
| 验证顺序 | 发泡剂相容 → 低温 → 内应力尺寸 → 气味抗菌 → 整机发泡 | 洗涤剂 ESC → 脱水疲劳 → 高温温冲 → 尺寸装配 → 整机 | 风险全部压到最后一步集中爆发 |
文字版结论：换料要动成型、工艺、外观三块，最该先谈验证顺序，其次内应力。内应力不写在物性表里，却决定件里留了多少，而它正是后面开裂的种子。
十、一页纸汇报对照表：内胆与内桶分两栏
结论先说：判断这张表是否合格只有一条——客户拿它，能不能在一次会上把两个件的材料方向一起定下来。
| 场景 | 推荐路线 | 关键指标 | 验证标准 | 需先确认的条件 |
|---|
| 【内胆】常规冰箱内胆（贴 PU 发泡） | 抗冲共聚 PP + 耐发泡剂体系 | 带应力发泡剂相容；−20~−30℃ 冲击 | 自定介质带应力浸泡；GB/T 1843 | 发泡体系、密度、发泡工艺温度 |
| 【内胆】高外观／尺寸要求段 | ABS／HIPS，或 PP 加表面处理 | 尺寸、表面、与 PU 层粘结 | 按件图与粘结验证 | 是否直触食物、抗菌要求 |
| 【内胆】直触食物内胆 | 食品级抗冲共聚 PP | 总迁移、高锰酸钾消耗、重金属、脱色 | GB 4806.7-2023 | 接触食品类别、使用温度 |
| 【内桶】家用洗衣机内桶 | 增韧改性 PP（耐洗涤剂体系） | 带应力洗涤剂 ESC；脱水循环疲劳 | ASTM D1693 / ISO 6252；循环台架 | 脱水转速、循环次数、洗涤剂 |
| 【内桶】高温或商用高负载内桶 | PP 不优先：不锈钢或增强工程塑料 | 疲劳、耐温、失圆 | 整机台架与程序口径 | 转速、负载、寿命要求 |
| 【内桶】需抗菌防霉内桶 | 增韧 PP + 抗菌防霉方案 | 抗菌活性、防霉等级 | ISO 22196 / ISO 16869；家电件对应口径 | 潮湿时长、防霉等级要求 |
文字版结论：同一台家电上"内胆走 PP、面板走 ABS、高端内桶走不锈钢"是正常配置。 靠的不是某一档更高，而是每个位置都对上自己的第一约束。
十一、冰箱内胆与洗衣机内桶上，最容易出问题的往往不是冲击
这两类件上最常见的归因偏差，是把"开裂"一律算在料脆上。公开机理清楚：冰箱发泡剂切到环戊烷类后，蒸气被 PP 基体吸收、使玻璃化温度下降并产生微泡，在残余应力下诱发环境应力开裂；内桶则是表面活性剂在应力协同下诱发银纹扩展，叠加脱水循环疲劳。
判据一侧，食品接触有硬线：GB 4806.7-2023 的总迁移、高锰酸钾消耗、重金属与脱色要求，2023 版还新增芳香族伯胺迁移总量不得检出（检出限 0.01 mg/kg）。
通行解法要分边：内胆侧先把耐发泡剂体系做够，再压低吸塑成型内应力、避开尖角过薄；内桶侧先把耐洗涤剂 ESC 体系做够，再上循环台架看疲劳。
宁波市科隆新材料有限公司在这两个件上常供的是自产改性聚丙烯（PP）造粒里的抗冲共聚方向（内胆）与增韧耐洗涤剂方向（内桶）：按发泡体系给耐发泡剂牌号，按脱水转速与循环次数配平增韧与耐 ESC，按是否直触食物给食品级全新料；配方按件工况调，可配合小样比对与台架对接。
这类询盘里，十次有七八次先问"冲击多少"，很少第一句问"发泡层用什么体系"或"脱水循环几千次"。而后者往往更早决定这个料能不能用。
常见问答
问：内胆开裂了，换一款更耐溶剂、增韧加满的料，是不是就能解决？
答：多半不能。主因是发泡剂从背面渗透，不是冲击韧性不够。要先看发泡体系、把耐发泡剂体系做够，再压低吸塑内应力、避开尖角过薄区。
问：洗衣机内桶只看缺口冲击值够高，是不是就稳了？
答：不够。内桶是被几千次脱水循环和洗涤剂共同磨开的，单次冲击值看不出疲劳寿命。要按转速与循环次数上台架，看径向变形、裂纹和紧固保持力。
问：内胆要直接接触食物，改性PP 能过食品接触吗？
答：可以，走食品级全新料并按 GB 4806.7-2023 验总迁移、高锰酸钾消耗、重金属与脱色。但食品接触合规和耐发泡剂相容是两本账。
| 工况 | 关键判据 | 自产常规供应 |
|---|
| 冰箱内胆（贴 PU 发泡） | 带应力发泡剂相容；−20~−30℃ 冲击 | 抗冲共聚 PP + 耐发泡剂方向 |
| 直触食物内胆 | GB 4806.7-2023 各项限值 | 食品级抗冲共聚 PP 方向 |
| 洗衣机内桶 | 带应力洗涤剂 ESC；脱水循环疲劳 | 增韧 + 耐洗涤剂改性 PP 方向 |
| 需抗菌防霉的内胆／内桶 | 抗菌 ISO 22196 / 防霉 ISO 16869 | 增韧 PP + 抗菌防霉方向 |
最后说三句。
第一，两个件都用改性PP，怕的东西却不是一个方向：内胆怕发泡层那一侧的渗透，内桶怕脱水循环疲劳加洗涤剂 ESC。
第二，选型第一句该问"发泡体系是什么、脱水循环几千次"，不是"冲击多少"。归因先分边，再换料。
第三，验证顺序比验证项更贵：内胆从发泡剂相容一票否决起，内桶从洗涤剂 ESC 一票否决起，两关都必须带应力试样，不许跳。
关于我们
件出问题，最常见的错法是先换料。
低温脆裂、翘曲、开裂、气味大——每一条的原因都不止一个，可能是基材档位错了，可能是成型条件没跟上，也可能确实是料的问题。先定位，再换料；顺序反了，往往换了几轮还在原地。
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 inner liner of the refrigerator is made of modified PP, and the inner drum of the washing machine is made of modified PP, but the things these two parts are afraid of are completely different: the liner is afraid of the foaming agent in the polyurethane foam layer on the back seeping in and causing cracking or blistering, while the inner drum is afraid of the fatigue from high-speed spin cycles combined with detergent ESC. This article separately discusses the six-dimensional working conditions, criteria, verification sequence, and reverse honesty for the two parts.
The material hasn't changed, the formula hasn't been altered, I've been using the refrigerator for half a year, and the inner liner cracked at the corner on its own.
A technician who works on freezers told me this. It wasn't caused by an impact; it slowly formed a fine crack, running along the corner, gradually spreading and getting longer.
Another engineer who makes washing machines said: After increasing the spin speed of the inner drum, several cycles ran, radial fine lines appeared on the drum wall, and the fixing screws also loosened.
Both parts are made of modified PP, and on-site failure looks like they both "broke brittlely," but the root causes are not the same. Treating these two parts as the same "PP parts" when selecting materials is the most common mistake in material selection for home appliances.
1. The inner liner of the refrigerator and the inner drum of the washing machine are both made of modified PP, but the things they are afraid of are not in the same direction.
Conclusion first: The failures of these two parts have completely different causes — the inner liner is mostly due to penetration on the foam layer side, while the inner tub is mostly due to the combined effects of fatigue and detergent.
If the inner liner has problems, it is mostly not due to insufficient impact toughness, but because the foaming agent slowly seeps in from the back and triggers it; if the inner tub has problems, it is mostly not shattered in one go, but wears down over thousands of dehydration cycles while soaking in detergent.
So below, we won’t mix them together; each of the two parts will have its own set of operating conditions and its own set of validations. This 'first separate the sides' judgment is more valuable than any formula recommendation—it directly determines whether you should first check the foam material or first check the rotation speed and cycle count.
2. Six dimensions of refrigerator inner liner working conditions: the compatibility of the foam layer is the watershed of this component
Conclusion first: In six dimensions, it is the 'medium' dimension that serves as the watershed for the inner liner, and this medium is not a detergent, but the layer of polyurethane foam on the back.
| Dimension | Actual operating conditions of the inner liner | Requirements for the materials |
|---|
| Temperature | Refrigeration 0~4℃, Freezing −18℃ Level 1; the temperature drops sharply from room temperature to the compartment temperature when the door is opened | Maintains toughness at low temperatures, does not crack |
| Load | Back pressure caused by foam layer expansion, liner self-weight, food load | As long as it is rigid and does not deform |
| Medium | Blowing agents (cyclopentane type, LBA type) in the polyurethane foam layer gradually permeate from the back; oils and food juices; wiping with cleaning agents | Foaming agent migration resistance (the most expensive dimension); oil-resistant, detergent-resistant |
| Lifespan | The entire machine is designed for 10-15 years of regular use | Does not crack, blister, or become brittle over time |
| Appearance | Smooth and easy to clean; odors absorbed by PP parts are difficult to remove | Low odor, easy to clean, no surface shrinkage |
| Compliance | Direct contact with food → GB 4806.7-2023; for antibacterial and mold-resistant, refer to separate household appliance component standards | Overall migration and other limit values meet the standards; antibacterial if necessary |
Text Version Conclusion: Temperature is not the hardest part; the medium is. The mechanism of 'crazing and blistering' is: small molecules of the blowing agent (cyclopentane vapor is the most typical) are absorbed by the PP matrix → plasticization and swelling, glass transition temperature decreases, microbubbles form locally → environmental stress cracking is induced under residual stress. The first question when selecting materials should be: 'What is the system of the foam layer, what is the density, and what is the process temperature range?'
A professional detail: Most liners are thermoformed (vacuum-formed) parts, and the residual internal stress is harder to release than in injection-molded parts. Uneven wall thickness also concentrates stress in thinner areas. With the same batch of material, injection-molded parts are fine, but vacuum-formed liners crack, often because the forming internal stress wasn’t relieved.
According to public statements, the main factors affecting penetration cracking are four: inner wall thickness, molding internal stress, material crystallinity, and the density and process window of the foaming material. There are three countermeasures applied together: choose a foaming agent grade that is resistant, control molding internal stress (sheet temperature, stretching ratio, and anneal if necessary), and structurally avoid sharp corners and overly thin areas. On the inner liner side, material is not a secondary issue—the compatibility between the foaming agent and the matrix itself is the direct answer in the dimension of 'medium.'
3. Six-dimensional operating conditions of the washing machine drum: high-speed spin fatigue and detergent are the two main causes
Conclusion first: the watershed of the inner drum is 'cyclic fatigue and detergent' — it is not broken by a single impact, but worn down by thousands of spin cycles and surfactants together.
| Dimension | Actual operating conditions of the inner drum | Requirements for the materials |
|---|
| Temperature | Washing from room temperature to high temperature (some programs 60-90°C), sudden drop in rinsing temperature | Temperature-resistant washing, long-term non-deformation |
| Load | High-speed dehydration centrifuge load: the higher the speed, the greater the centrifugal force; imbalance is normal, and dynamic balance imbalance will amplify local loads. | Resistant to long-term cyclic fatigue, dynamically balanced and stable |
| Medium | Detergent and fabric softener long-term contact (surfactants), residues remain after rinsing | Detergent-resistant ESC |
| Lifespan | Designed according to the number of dehydration cycles (commonly several thousand to over ten thousand per stage) | Test according to the number of cycles, not according to the single-cycle limit |
| Appearance | Stain-resistant, easy to clean, does not hold dirt | Smooth surface, antibacterial and mildew-resistant |
| Compliance | Used in humid water systems; commonly for antibacterial and antifungal purposes | Mildew resistance level; washing machine components according to household appliance antibacterial standards |
Text version conclusion: The dimension of load pertains to cyclic fatigue, not static strength. The higher the rotational speed and the greater the centrifugal load, after long-term cycling, deformation, cracking, or loosening of fastening points may occur. Looking at single impact values does not reveal problems; it is necessary to use a cycling test bench and record results according to the number of cycles.
A professional detail: The inner tub is an injection-molded part, usually selected with MFR 20-40 g/10min (GB/T 3682 caliber). Its internal stress comes from the gate, holding pressure, and rib positions; even more critical is the dynamic balance—if the tub body is slightly off-center, the system resonates during spinning, directly reducing fatigue life. The 'material' of the inner tub should be considered together with 'structure and dynamic balance'.
4. Material route division: Each pipe section for impact copolymer PP, toughened modified PP, ABS/HIPS, and stainless steel inner drum.
Conclusion first: these four routes are not alternatives, but complementary roles—low temperature and vacuum forming for PP inner liners with impact copolymerization, toughness and detergent resistance for PP inner tubs with toughening modification, surface and dimensional considerations for ABS/HIPS, and durability for stainless steel inner tubs.
| Route | Get what | Cost | Suitable for which section |
|---|
| Impact-resistant copolymer PP (main liner material) | Low-temperature resistant, easy to thermoform and vacuum form, suitable for food contact | Foam retardants require specialized systems; ordinary impact-resistant copolymers cannot block the penetration of cyclopentane compounds. | Refrigerator liner, drawers, fruit and vegetable boxes |
| Toughened modified PP (main material for inner barrel) | High toughness, resistant to detergent ESC, can be injection molded into complex rib positions | Fatigue life depends on wall thickness and structural reinforcement; after adding minerals or fiberglass, the surface becomes rougher | Washing machine inner drum, agitator, outer drum |
| ABS / HIPS (common liner alternatives) | Good surface, easy to shape, stable dimensions | Temperature resistance is average; bonding with the PU foam layer requires additional treatment | Inner liner section with high requirements for appearance and dimensions |
| Stainless steel inner tub | Fatigue-resistant and corrosion-resistant | High cost, heavy weight, not part of the PP system | High-load inner drum, commercial models |
Text version conclusion: PP joint is 'light, low cost, chemically resistant, easy to mold'; ABS/HIPS joint is about 'surface and dimensions'; stainless steel joint is 'durable'. It is common for several different materials to each handle a section on the same refrigerator or washing machine. Material selection only describes their division of labor, without giving a conclusion of 'which is better'.
The boundaries need to be clarified: if the inner liner is in long-term contact with a highly polar foam system, the material system is more critical than the amount of toughening; if the inner barrel aims for high speed and long life, the fatigue limit of PP will be reached first, and it needs to be compensated with wall thickness, ribs, dynamic balance, and fastening design.
5. ★ Selection Criteria Table: Inner liner and inner bucket listed separately, each item with a verification method
Conclusion first: The value of this table lies in the third column — what usually holds you back is not 'which item to look at,' but 'what to measure and what amount counts as passing'.
| Indicator | Threshold Value (Typical) | Verification Method · Standard Number | Common Failures | Common solution |
|---|
| [Liner] Resistant to foaming agents compatibility (with stress) | The stressed specimen does not crack or blister under the actual blowing agent environment | Stress soaking of the medium should be determined according to the actual foaming system; stress loading can refer to the approaches of ASTM D1693, ISO 6252, and ISO 22088-3. | Corner fine lines, bulges, cracks | Foaming agent-resistant system Controls molding internal stress Prevents excessive thinning at sharp corners |
| [Inner Liner] Low Temperature Shock | Keep by item: −20~−30℃ to maintain toughness | GB/T 1843 (Cantilever beam, equivalent to ISO 180 system) | Cracks caused by temperature difference between freezing and door opening | Impact Copolymer Toughening System |
| [Inner Liner] Food Contact | Overall migration ≤10 mg/dm², potassium permanganate consumption ≤10 mg/kg, heavy metals (calculated as Pb) ≤1 mg/kg, color removal negative; for materials containing aromatic isocyanates or azo dyes, the total migration of aromatic primary amines must not be detected (detection limit 0.01 mg/kg) | GB 4806.7-2023 (Methods GB 31604.8 / .2 / .9 / .52) | Non-compliant | Food-grade virgin material Controls low molecular weight elution |
| [Inner liner] Odor and antibacterial and antifungal | Low odor, antibacterial activity, and anti-mold grade are determined per item | Antibacterial ISO 22196:2011 / GB/T 31402-2015 film method (24 h); anti-mold ISO 16869:2008 / ASTM G21 (28°C, 14 days); for household appliance parts, see GB 21551.4-2010 | Odor adsorption, mold spots | Low-odor system Silver ion/zinc-based antibacterial agent |
| [Inner Drum] Resistant to Detergent ESC (with Stress) | The stressed specimen does not crack in the detergent up to the target duration | Bent strip method ASTM D1693 (10% Igepal CO-630, 50±0.5℃, recorded as F₅₀); Constant tensile stress method ISO 6252 | Radial fine lines on the barrel wall | Detergent-stable system |
| [Inner Drum] Dehydration Cycle Fatigue | By the number of cycles: radial deformation, cracks, and loosening of fastening points do not exceed the limit | Dehydration circulation test bench (by dehydration speed and number of cycles) | Radial cracks, loose fastening, out-of-round | Wall thickness Reinforcement rib Dynamic balance Fastening design |
| [Inner Tub] Temperature Resistance and Size | Long-term temperature resistance without deformation; shrinkage rate meets the clearance with the outer shell and the fit with the impeller/drum | GB/T 1634 (Heat Deflection Temperature); GB/T 17037.4 / ISO 294-4 | High temperature out-of-round; assembly misalignment, gap out of tolerance | Enhanced system control HDT Mineral-filled shrinkage control, look at the gate first |
Text version conclusion: The first and fifth rows should be done first, and both rows must include stressed samples. There are existing reports for tensile, impact, and shrinkage tests. For medium immersion, the medium, stress, and time must be determined by ourselves—if everything before passes but this step fails, the entire batch plan is void.
The inner barrel has another component-level reference specification: MFR 20-40 g/10 min (GB/T 3682 standard), notched impact >6 kJ/m² at 23°C, >3 kJ/m² at −20°C, flexural modulus >1667 MPa. On the media side, there is a publicly available magnitude anchor: a commercial impact-resistant copolymer grade was recorded to have no cracking for over 500 hours at 10% Igepal, 50°C — this is an anchor, not a threshold. The criterion is written in three elements: temperature, duration, result.
6. Common Failures and Root Causes: The inner liner often cracks starting from the foam side, and the inner drum often cracks due to fatigue and detergents.
Conclusion first: The attribution of these two parts is completely different, and confusing them is the root cause of repeated rework in material selection.
Failure 1: Fine cracks and blisters in the inner liner corners. The root cause is mostly not 'the material is too brittle,' but the foaming agent seeping from the back, causing plasticizer swelling, which cracks under residual stress. Can we deny a common practice: attributing this to 'the material is not tough enough, add a toughening agent' is wrong. Toughening cannot prevent small molecule penetration — what needs to be addressed is a foaming agent-resistant system, while also reducing thermoforming internal stress and structurally avoiding sharp corners and overly thin areas.
Failure 2: Radial micro-cracks in the inner drum and loose fastening points. The root cause is cyclic fatigue combined with detergent ESC. Similarly, can we deny a common practice: judging the inner drum material only by a single impact value is not sufficient. It is necessary to test on a stand according to the number of spin cycles, to observe deformation, cracks, and fastening retention after thousands of cycles.
Failure Three: Odor inside the liner, mildew spots in the inner drum. The former occurs because the PP parts absorb odors that are difficult to remove, and the latter occurs because the inner drum remains damp for a long time and the anti-mold level is insufficient. Both rely on a low-odor system combined with bacteria reduction/mold prevention solutions, verified according to ISO 22196 / ISO 16869.
A new judgment. Many articles discussing cracking directly treat "reducing internal stress and modifying structure" as the first solution. For these two matters, there is a more crucial prior step: first identify which side is the cause — causes from the inner liner are mostly on the foam layer side, while causes from the inner barrel are mostly due to the combined effect of fatigue and detergent. First determine the side, then change the material; if the order is reversed, you'll keep ending up in the same place even after several rounds of changes.
7. Verification sequence: The refrigerator inner liner and the washing machine inner drum are two separate processes
Conclusion first: There is only one principle - put the step that is most likely to veto and also most easily overlooked at the front; the first step of the two items is not the same step.
Refrigerator inner pot verification sequence (Foaming agent compatibility veto):
'
(1) Foaming agent compatibility (with stress) Determine the medium according to the actual foaming system; Sample with stress; Mark "cracked/non-cracked + bulge + appearance change"
↓ However, no further steps are needed; Return to the foaming agent system + internal stress and structure of molding
(2) Low-temperature impact −20~−30°C notch impact, specimen status according to GB/T 1843
↓ However, return to impact resistance copolymer level and toughness gain
(3) Internal stress and dimensions after thermoforming Residual stress, wall thickness distribution, shrinkage and assembly clearance
↓ However, Return molding process (sheet temperature/tensile ratio/annealing) and wall thickness design
(4) Odor and antibacterial and anti-mold low-odor acceptance + antibacterial ISO 22196 / anti-mold ISO 16869
↓ However, return to low-odor system and antibacterial agent solution
(5) Full-machine foaming verification: After installation, perform real foaming, observe the interface between the inner tank and foam layer
↓ If not compliant, return to (1) rearrangement system
'
Washing Machine Inner Drum Validation Order (Detergent ESC Veto):
'
(1) Detergent ESC (with stress) Determine the medium according to the actual detergent; Bending method ASTM D1693 / Constant tensile stress method ISO 6252
↓ However, no further steps are needed; Return to detergent-resistant system
(2) Dehydration cycle fatigue: Place on the bench according to spin speed and cycle count; Measure radial deformation, cracks, and fastening retention force
↓ However, retract wall thickness/reinforcement/dynamic balance/fastening design
(3) High temperature and thermal flushing High-temperature washing program + rinse temperature drop cycle, measure deformation and round loss
↓ However, return reinforcement system and temperature resistance range
(4) Dimensions and assembly shrinkage rate, clearance with housing, coordination with puleller/drum
↓ However, Return filling amount and gate position
(5) Whole machine operation verification: Full machine washing + spin cycle, long-term observation
'
Text version Conclusion: The inner tank is most likely to leak (1) (foaming agent compatible), the inner drum is most likely to leak (1) (detergent ESC); both stages require stress samples. The most common mistake is to soak a stress-free sample in medium—soaking for a long time without issue, but cracking after one week of stress, essentially leaving the crack for half a year after installation.
8. Reverse honesty: In these three situations, this piece should not be made of modified PP
Conclusion: First: As long as requirements like "long-term contact with strongly polarized media and no cracking" or "high transparency" coexist, it means the part should not be supported with modified PP.
| Situation | Why is modified PP unsuitable ? | Where should it go ? |
|---|
| The inner liner should be long-term applied to a strong polar foaming system, and must never crack or bulge | Ordinary impact-resistant copolymer, even if fully toughened, cannot block the long-term penetration of small foaming molecules | using specially proven composites with proven compatibility; Alternatively, add a separation layer and modify the metal inner tank plan |
| Washing machine inner drum requires long-term high temperature + high-intensity dehydration (commercial, industrial-grade high speed and high load) | PP has upper limits on temperature resistance and fatigue life. After the centrifugal load reaches the top, radial cracks are difficult to control | stainless steel inner drum, or fiberglass reinforced engineering plastic inner drum |
| inner tank requires high transparency (display cabinet, Depends on the food use) | PP Semi-transparent, transparent grades with limited haze | transparent PETG/PC or glass liner |
text version Conclusion: It's not that modified PP can't achieve one thing, but that it can't achieve "strong polar foam with long-term contact + absolutely no cracking" or "high transparency + PP" — two things in opposite directions at the same time. Orders that are forced to follow up will eventually be returned through rework and claims.
9. Material Change Risk Checklist: The things to confirm between the blister and injection molded inner drum are different
Conclusion First: The customer's real concern is often not performance, but "Should I change my current mold and process"—the inner tank is vacuum-formed, the inner drum is injection-molded, so the items to confirm are not exactly the same.
| Items to be moved | Inner tank (vacuum forming) to confirm | Inner barrel (injection molding) to confirm | What happens if not done |
|---|
| Molding shrinkage rate | Vacuum forming tensile ratio and rebound, wall thickness distribution | Injection molding shrinkage rate and long part dimensions, GB/T 17037.4 | Size deviation, assembly mismatch |
| Mold and vent | Vacuum forming mold surface and air circuit | gate position, vent (appearance parts are more sensitive) | Insufficient filling, weak fusion line |
| Material temperature and mold temperature | Sheet temperature and vacuum forming mold temperature window | Material temperature/mold temperature and residence time | Decomposition, excessive internal stress |
| Drying | Specific system requirements | Specific system requirements | Silver wire, bubbles |
| Holding pressure and demolding | Annealing reduces residual stress | Pressure retention determines internal stress, ejection prevents strain damage | High internal stress raises cracking risk |
| Color difference | Light inner tank first color panel | Light inner barrel first sets color board | Batch color difference dispute |
| Verification sequence | Foaming agent compatibility → low-temperature → Internal stress dimensions: → Odor and antibacterial → Whole machine foaming | Detergent ESC → Dehydration fatigue → High-temperature thermal stamping → Dimensional assembly → Whole machine | Risks are suppressed to the last step concentrated explosively |
Text version Conclusion: Material change requires three aspects: forming, process, and appearance. The first step should be the verification sequence, followed by internal stress. Internal stress is not written in the physical property table, but it determines how much remains in the piece, and it is precisely the seed that cracks later.
10. One-Page Report Comparison Table: Inner Pot and Inner Barrel Separated in Two Columns
Conclusion First: There is only one way to judge whether this form is qualified—the customer takes it and can determine the material directions for both pieces together at a single meeting.
| Scenario | Recommended route | Key indicators | Verification standards | Conditions to be confirmed first |
|---|
| 【Inner pot】Standard refrigerator inner pot (PU foaming) | Impact copolymer PP + foam-resistant system | Stress-resistant foaming agent compatible; −20~−30°C impact | Custom medium stress soaking; GB/T 1843 | Foaming system, density, foaming process temperature |
| [Inner Liner] High Appearance/Size Requirement Section | ABS/HIPS, or PP with surface treatment | Size, Surface, and Bonding with PU Layer | Verification of Parts Drawings and Bonding | Direct contact with food or antibacterial requirements |
| [Inner Liner] Direct contact with food inner liner | Food-grade impact-resistant copolymer PP | Total migration, potassium permanganate consumption, heavy metals, decolorization | GB 4806.7-2023 | Food contact category, usage temperature |
| [Inner Tub] Inner Tub of Household Washing Machine | Toughened modified PP (detergent-resistant system) | Stress-bearing detergent ESC; dehydration cycle fatigue | ASTM D1693 / ISO 6252; cyclic testing rig | Spin speed, number of cycles, detergent |
| [Inner Drum] High-temperature or commercial heavy-duty inner drum | PP not preferred: stainless steel or reinforced engineering plastics | Fatigue, temperature resistance, out-of-roundness | Whole machine test bench and program caliber | Speed, load, and lifespan requirements |
| [Inner Drum] Requires an antibacterial and mildew-resistant inner drum | Toughened PP Antibacterial and Mildew-Proof Solution | Antibacterial activity, mildew resistance level | ISO 22196 / ISO 16869; Corresponding caliber for home appliance parts | Duration of humidity, mold resistance level requirements |
Text version conclusion: On the same household appliance, 'the inner drum uses PP, the panel uses ABS, and the high-end inner barrel uses stainless steel' is a normal configuration. It doesn't rely on a higher grade of one material, but rather each position meets its primary constraint.
11. On the inner liner of the refrigerator and the inner drum of the washing machine, the parts most prone to problems are often not due to impact.
The most common attribution bias for these two types of parts is to attribute all 'cracking' to material brittleness. The mechanism is clear: when the refrigerator foaming agent comes into contact with cyclopentane, the vapor is absorbed by the PP matrix, lowering the glass transition temperature and generating microbubbles, which under residual stress induce environmental stress cracking; for the inner tub, surfactants, under the synergy of stress, induce silver streak propagation, combined with fatigue from dehydration cycles.
On the criteria side, there are strict requirements for food contact: overall migration, potassium permanganate consumption, heavy metals, and decolorization according to GB 4806.7-2023. The 2023 version also newly requires that the total migration of aromatic primary amines must not be detected (detection limit 0.01 mg/kg).
The conventional solution requires separating the sides: on the inner liner side, first apply enough of the foaming-resistant agent system, then reduce thermoforming internal stress and avoid overly thin areas at sharp corners; on the inner drum side, first apply enough of the detergent-resistant ESC system, then test fatigue on the cycling bench.
Ningbo Kelong New Materials Co., Ltd. commonly supplies two types of self-produced modified polypropylene (PP) granules: the impact-resistant copolymer type (for inner liners) and the toughened detergent-resistant type (for inner tubs). The foam-resistant grade is provided according to the foaming system; toughness and ESC resistance are balanced according to dehydration speed and circulation times; food-grade virgin materials are provided depending on whether they come into direct contact with food. Formulations are adjusted according to component working conditions and can be compared with small samples and coordinated on the test bench.
In this type of inquiry, seven or eight times out of ten, the first question is usually 'How much impact?' and rarely the first question is 'What system is used for the foam layer?' or 'How many thousand cycles of dehydration?' The latter often determines earlier whether the material can be used.
Frequently Asked Questions
Question: The inner liner has cracked. If we switch to a material that is more solvent-resistant and tougher, will that solve the problem?
Answer: Most likely not. The main reason is that the foaming agent permeates from the back, not because the impact toughness is insufficient. You need to first check the foaming system, ensure the system is resistant to the foaming agent, then reduce the thermoforming internal stress and avoid thin areas at sharp corners.
Question: If the inner drum of the washing machine only looks at the notch impact value being high enough, does that mean it is stable?
Answer: Not enough. The inner drum is worn by thousands of dehydration cycles and detergents together, so the fatigue life cannot be determined from a single impact test. It needs to be tested on a bench according to rotational speed and number of cycles, observing radial deformation, cracks, and fastener retention.
Q: The liner will come into direct contact with food. Can modified PP pass food contact requirements?
Answer: Yes, using all new food-grade material and testing overall migration, potassium permanganate consumption, heavy metals, and decolorization according to GB 4806.7-2023. However, food contact compliance and compatibility with foaming agents are two separate issues.
| Operating condition | Key criterion | Self-produced regular supply |
|---|
| Refrigerator inner liner (PU foam laminated) | Compatible with stress-foaming agent; −20~−30℃ impact | Impact-resistant copolymer PP Oriented towards anti-foaming agent |
| Direct contact with the food inner container | GB 4806.7-2023 Various Limit Values | Food-grade impact-resistant copolymer PP orientation |
| Washing machine inner drum | Stress-bearing detergent ESC; dehydration cycle fatigue | Toughened detergent-resistant modified PP direction |
| Inner liner/inner tub that requires antibacterial and mold-resistant properties | Antibacterial ISO 22196 / Mildew-proof ISO 16869 | Toughened PP Antibacterial and Mildew-Resistant Direction |
Lastly, say three sentences.
First, both parts use modified PP, but the things they are worried about are in different directions: the inner liner is worried about penetration on the foam layer side, while the inner bucket is worried about dehydration cycle fatigue plus detergent ESC.
Second, the first question when choosing a model should be 'What is the foaming system, and how many thousands of dehydration cycles?' rather than 'How much impact?'. Attribution should first differentiate sides, then change the material.
Third, the verification sequence is more expensive than the verification items: the inner liner must undergo a veto check for compatibility with the foaming agent, and the inner bucket must undergo a veto check with the detergent ESC. Stress samples are required for both stages, and skipping is not allowed.
About Us
When a part has a problem, the most common mistake is to change the material first.
Brittle at low temperatures, warping, cracking, strong odor—each issue has more than one possible cause. It could be that the base material grade is wrong, the molding conditions were not followed, or indeed there is a problem with the material. First identify the cause, then change the material; if the order is reversed, you often end up cycling through several changes and still remain in the same situation.
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.
