密封垫圈与卫浴洁具壳体用改性PP，最容易漏看的两个判据是压缩永久变形和耐洗涤剂 ESC。这篇把 TPV 的两相结构讲透，给出垫圈"硬度不是寿命决定项"的反直觉结论，以及卫浴壳体耐环境应力开裂的三要素、验证顺序与换料清单。
"我们做的卫浴水龙头壳体，刚装半年，浅色面就发白，还裂了一道缝，是不是料不耐？"
"垫圈按硬度选了 70A 的，装上三个月就漏水。硬度不是够硬吗，怎么还漏？"
这两个问题我来来回回被问过很多次。问的人以为这是两件事——一个裂、一个漏，但其实根因指向同一个选型盲区：垫圈盯着硬度和拉伸强度选，卫浴壳体盯着颜色和刚性选，谁都没把"长期压缩后还能不能弹回来"和"长期泡清洁剂会不会开裂"当主线。
下面按工况、路线、判据、验证四层往下拆。先说一个本篇最重要的结构知识点。
一、密封垫圈漏水和卫浴壳体发白，根因都出在"把 TPV 当成加软的 PP"
先纠正一个最常见的误解：密封垫圈材料（TPV）不是"加软的 PP"，它是聚丙烯（连续相）+ 交联 EPDM（分散相）动态硫化出来的两相体系。
这一点是本篇所有判断的地基，必须讲透。动态硫化（dynamic vulcanization）的过程是：在高温高剪切下，EPDM 橡胶相交联成微米级颗粒，然后均匀分散在 PP 连续相里。结果就是——PP 连续相贡献了耐热、耐候、可注塑回收的塑料特性；交联 EPDM 分散相贡献了橡胶的回弹和密封性。所以它既不像纯 PP 那样硬而脆，也不像传统硫化橡胶那样只能硫化、不能注塑。
一个同行抄不走的判断：TPV 的性能来自"两相比例 + 交联程度"这两个变量，不是来自"PP 软不软"。同样标着 70A 硬度的 TPV，EPDM 相比例低一点、PP 相比例高一点，压缩后的回弹表现可以差出一截——这就是为什么两个牌号硬度一样、垫圈寿命却差很多。只看硬度选料，等于只看了配方里的一个角。
卫浴洁具壳体走的则是另一条路：它要的是刚性外观件，不是弹性密封件，所以主体是抗冲共聚改性PP，必要时加矿物/滑石粉填充补刚性、加助剂提耐清洁剂稳定性。后面会讲，它的失效主角不是回弹，是环境应力开裂（ESC）。
二、工况六维拆解：垫圈长期压缩 + 洁具长期泡清洁剂，六个维度给数字
垫圈和卫浴壳体虽然都姓"PP 系"，工况却完全不同。把六维报齐，方向才出得来。
| 维度 | 密封垫圈（TPV）的实际工况 | 卫浴洁具壳体（改性PP）的实际工况 | 对材料的要求 |
|---|
| 温度 | 工作 23-70℃；冬季安装可到 −20~−30℃ | 长期接触 40-60℃ 热水，混水阀/喷头附近瞬时 80-95℃ | 垫圈看低温回弹；壳体看耐热与热应力 |
| 载荷 | 设计压缩率 15-25%（GB/T 7759 常用 25%） | 装配预紧 + 注塑残余应力，需控制在低位 | 垫圈看压缩永久变形；壳体看残余应力 |
| 介质 | 机油/润滑脂（卫浴五金）、水；部分接触弱清洁剂 | 清洁剂/表面活性剂浓度常见 1-10%，强碱洁厕剂 pH>12 | 垫圈看体积变化率；壳体看耐 ESC |
| 寿命 | 反复压缩 1×10⁴-5×10⁴ 次不失效 | 设计寿命常见 5-10 年（约 1.8-3.6×10⁴ h） | 垫圈看回弹保持；壳体看长期不开裂 |
| 外观 | 多为深色弹性件，外观要求低 | 常做免喷涂浅色外观面，ΔE 需受控 | 浅色面禁裂、禁霉斑、禁色差 |
| 合规 | 饮用水/食品接触件需 GB 4806；可回收 | 抗菌件需 GB/T 31402-2015；食品级需 GB 4806 | 按用途定标准，不混用 |
六个维度里，垫圈的一票否决项是压缩永久变形，壳体的一票否决项是耐 ESC——这两个判据在贸易版和已有家电篇里都没被当成主线讲过，本篇就落在它们身上。
一个内行细节：压缩永久变形率的算法是 CS = [(h₀ − h₁) / (h₀ − hₛ)] × 100%，其中 h₀ 是原始厚度、h₁ 是恢复后厚度、hₛ 是限制器（压缩状态）高度。同一批料，压缩率用了 25% 还是 30%、保温 22h 还是 70h，出来的数能差很多。所以谈压缩永久变形，不报"温度 + 时间 + 压缩率 + 标准号"四个条件，这个数没有比较意义。
三、两条路线并列：垫圈走 TPV，卫浴壳体走耐 ESC 共聚 PP
同一个"PP 系"，垫圈和壳体落在两条完全不同的路线上。这里只做分工陈述，不排谁更好。
| 路线 | 材料形态 | 拿到什么 | 付出的代价 / 边界 |
|---|
| 密封垫圈材料（TPV，PP/EPDM 动态硫化） | 两相体系，PP 连续相 + 交联 EPDM 分散相 | 橡胶回弹 + 可注塑回收 + 耐候耐臭氧 | 耐高温上限约 100-135℃（视牌号）；耐芳烃溶剂差 |
| 耐 ESC 抗冲共聚 PP（矿物/滑石粉填充） | 均相/半相 PP + 抗冲共聚 + 填充 | 刚性外观 + 耐清洁剂稳定 + 免喷涂浅色面 | 本身是刚性件，没有密封回弹；依赖 ESC 评价把关 |
| 传统硫化橡胶（EPDM/NBR/FKM，作对照） | 硫化交联网络 | 专一介质耐受更强（尤其 FKM 耐溶剂、NBR 耐油） | 不可注塑、不可回收、成本高、需硫化工序 |
分法很朴素：要回弹密封，走 TPV；要刚性外观又长期泡清洁剂，走耐 ESC 共聚 PP。 两者不是替代关系，是同一卫浴组件里"动件"和"静件"的分工——垫圈负责封、壳体负责撑。
敢否定一个常见做法：有人为了"省事"，拿普通 PP 甚至随便一款填充 PP 去做密封垫圈。这是错的。普通 PP 是刚性塑料，没有交联橡胶相，受压后基本不回弹，它根本不具备密封所需的弹性恢复能力——垫圈该出现在 TPV 这类热塑性硫化胶上，不是刚性 PP 上。
四、★ 选型判据表：压缩永久变形 + 耐 ESC，每个判据都带验证方法
下面这张表是全篇最该收藏的部分。注意第四列"验证方法·标准号"——选型时最常卡住的不是"看哪个指标"，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 |
|---|
| 压缩永久变形（70℃×22h，25% 压缩） | ≤25-30%（据公开牌号资料，B 级） | GB/T 7759.1-2015 / ISO 815-1:2019；ASTM D395-18 方法 A（恒定压缩率） | 松开后回弹不足、密封间隙漏水 | 选交联度合适的 TPV、控制 PP 相含量 |
| 低温压缩永久变形（−20~-30℃×22h） | 越低越好，据 GB/T 7759.2-2019 / ISO 815-2:2019 | GB/T 7759.2-2019 / ISO 815-2:2019 | 冬季安装后弹不回、冷装渗漏 | 提高 EPDM 相比例、复核基材档位 |
| 耐介质体积变化率（浸泡后） | 机油浸泡膨胀率据公开资料约 ≤8%（B 级）；清洁剂浸泡需受控 | GB/T 1690 / ISO 1817 + GB/T 7759.1 浸泡法 | 膨胀变软、被挤出密封槽 | 控制 PP 相比例、选耐介质牌号 |
| 环境应力开裂 ESC（卫浴壳体） | 通过评价：ASTM D1693 50℃、10% Igepal CO-630 下 F₅₀ 时间越长越好；ISO 22088-3 临界应力越高越好 | ASTM D1693（弯条法）；ISO 22088-3（恒拉伸应力法，40℃）；ISO 6252（恒应变法，1.0-2.0% 应变，50-80℃） | 浅色面发白、沿应力集中处开裂 | 抗 ESC 共聚 PP + 控注塑内应力 |
| 硬度（邵氏 A） | 垫圈 40-80 Shore A，按密封力反推 | GB/T 531.1 / ISO 7619-1 | 压不动或压塌 | 按压缩力设计，不单看硬度 |
| 抗菌率（卫浴浅色面） | 抗菌活性值按贴膜法达标 | GB/T 31402-2015 / ISO 22196:2011（贴膜法，24h）；防霉 ISO 16869:2008 / ASTM G21 | 浅色面长霉斑、影响观感 | 银/锌系无机抗菌剂 + 耐久验证 |
文字版结论：六行里 压缩永久变形和 ESC 是最该先看的两项——前者决定垫圈"松开还能不能弹回来"，后者决定壳体"泡清洁剂会不会裂"。硬度、抗菌都是辅助判据，不能反过来喧宾夺主。把这张表当体检单，缺一项不判合格，比装上去再漏、再裂省钱得多。
五、常见失效与根因：四个现象，四条根因
失效一：垫圈按硬度选、三个月就漏。 根因几乎都在"盯硬度、不盯压缩永久变形"。硬度只决定"压得动压不动"，压缩永久变形才决定"松开之后还能不能弹回来"——后者才是密封寿命的决定项。这是行业里非常常见的一处错做法：把硬度当成了密封件的全部选材依据。
失效二：卫浴壳体长期泡清洁剂后发白、开裂。 根因是环境应力开裂（ESC），而且必须三要素同时在场才发生：应力（装配内应力 + 注塑残余应力）+ 介质（洗涤剂、表面活性剂、皂液）+ 时间。少一个都不会裂。公开资料里记录的机理是：表面活性剂在应力协同下诱发银纹扩展，最终开裂（据公开检测机构技术资料，B 级）。
失效三：垫圈耐介质后体积膨胀、被挤出密封槽。 根因是 PP 连续相被油类/溶剂溶胀。TPV 里 PP 相比例越高，对矿物油、芳烃的耐受越差。同一硬度、不同 EPDM/PP 比例的牌号，耐油性可以差出一档。
失效四：免喷涂浅色壳体既开裂又色差。 归因要分两步：开裂先看 ESC 与残余应力，色差先看色母与批次。抗菌剂管的是霉斑，不是开裂——加了抗菌剂的浅色件照样会因为 ESC 裂，这两件事别混为一谈。
六、验证顺序：先验什么，后验什么
这一段同行几乎没人写，但它是换料能不能省钱的关键。顺序错了，成本会在最后一步集中爆出来。
`
① 小样物理比对 硬度 / 拉伸 / 断裂伸长 / 体积密度
↓ 基础项在门限内，才往下走
② 压缩永久变形 TPV 垫圈：70℃×22h（25% 压缩）先过
↓ 这一关不过，后面全部不用做
③ ESC 评价 卫浴壳体：ASTM D1693 / ISO 22088-3 / ISO 6252
↓ 临界应力/开裂时间不达标，退回选材
④ 低温回弹验证 −20~-30℃×22h 压缩永久变形（GB/T 7759.2）
↓ 冬季安装件必过
⑤ 短射试模 看充填、熔接线、内应力分布、浅色面表现
↓ 短射走通，才谈批量
⑥ 批量试产 + 客户端验证
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每一步都有明确的"不过就退回上一级"的判据。最常见的错误是跳过 ② 和 ③ 直接进 ⑤，用试模件去判断材料性能——试模件的成型条件往往是临时的，测出来的数没有代表性，等装上现场才发现漏或裂，损失已经是整批。
文字版结论：验证顺序是 小样 → 压缩永久变形 → ESC → 低温回弹 → 短射 → 批量。压缩永久变形和 ESC 这两关必须在试模之前过，因为它们是最可能一票否决的项；过了再做模具侧的事，才不会白花试模费。
七、反向诚实：这三种情况，这个件不该用改性PP（TPV 也不够）
前面讲"怎么做"，这里讲"什么时候别做"。这一段对选型判断的价值最高。
| 出现的情况 | 为什么改性PP / TPV 不合适 | 该往哪走 |
|---|
| 要求长期接触强溶剂或高浓度强表面活性剂（如芳烃、氯化溶剂、高浓度强碱持续浸泡） | PP 连续相对这类介质耐受有限，体积变化与溶胀难以压住 | 氟橡胶 FKM（耐溶剂）、丁腈橡胶 NBR（耐油）或专用耐蚀弹性体 |
| 要求长期高温密封（持续 100℃ 以上，甚至 135℃ 以上常态） | TPV 耐温上限约 100-135℃（视牌号），持续超温会加速永久变形与老化 | 硅橡胶（耐温更宽）或氟橡胶 FKM |
| 要求极高压缩回弹精度（如精密液压密封、高压动态密封） | TPV 的压缩永久变形与应力松弛精度，达不到精密液压密封的量级 | 丁腈橡胶 NBR、氟橡胶 FKM 或专用液压密封弹性体 |
规律很清楚：凡是"介质强度、温度、回弹精度"任一项踩到 PP 系边界的，就说明这个密封件不该用改性PP（含 TPV）硬撑。 遇到这种需求，我们的做法是先把这条讲清楚，再谈有没有折中——硬接下来的单子，最后都要用返工和索赔还回去。
八、换料要动什么：一张先看再动的清单
决定试改性PP（或把现有料换成 TPV/耐 ESC 共聚 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 | TPV 与刚性 PP 收缩率不同，密封槽/壳体尺寸需核对 | 尺寸超差，装配对不上或密封槽过紧 |
| 浇口与排气 | TPV 流动与弹性回复特性不同，壳体浇口位置影响内应力 | 充填不足、残余应力集中引发 ESC |
| 料温与模温 | TPV 注塑 175-210℃（据公开牌号资料，B 级）；壳体模温影响内应力 | 表面缺陷、内应力过高、ESC 风险上升 |
| 干燥 | TPV 多数免干燥（可选 80℃×3h）；壳体按体系定 | 银丝、气泡、浅色面瑕疵 |
| 保压与脱模 | 弹性体回弹与刚性件脱模逻辑相反 | 变形、顶出拉伤、弹性件粘模 |
| 色差 | 免喷涂浅色壳体必须先确认色板再上机 | 批次色差争议、浅色面观感不达标 |
| 验证顺序 | 小样 → 压缩永久变形 / ESC → 短射 → 批量 | 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 ESC/压缩永久变形直接批量，一次失效就是整批召回级损失。
九、一页纸汇报表（可以直接贴进 PPT）
| 场景 | 推荐路线 | 关键指标 | 验证标准 | 需先确认的条件 |
|---|
| 建筑/卫浴密封垫圈 | TPV（PP/EPDM 动态硫化） | 压缩永久变形 ≤25-30%（70℃×22h）；低温回弹达标 | GB/T 7759.1 / ISO 815-1；GB/T 7759.2 / ISO 815-2 | 工作温度、压缩率、接触介质 |
| 卫浴洁具壳体（浅色免喷涂） | 耐 ESC 抗冲共聚 PP + 矿物填充 | ESC 通过评价；浅色面不开裂、ΔE 受控 | ASTM D1693 / ISO 22088-3 / ISO 6252；GB/T 531.1 | 清洁剂类型与浓度、装配应力 |
| 免喷涂抗菌壳体 | 耐 ESC 共聚 PP + 无机抗菌剂 | 抗菌活性值达标；防霉等级 | GB/T 31402-2015 / ISO 22196；ISO 16869 | 抗菌与 ESC 双指标同时验收 |
| 冬季安装/低温工况垫圈 | TPV（高 EPDM 相比例） | 低温压缩永久变形达标 | GB/T 7759.2 / ISO 815-2 | 当地最低气温记录 |
文字版结论：这张表的作用是让技术员能把结论直接往上报，不必重新组织语言。判断标准只有一条——客户拿这张表，能不能在一次会议里把材料方向定下来。
十、这个件上最容易出问题的，往往不是料
卫浴与密封件上行业最常见的一类早期失效，是壳体长期接触清洁剂后发白开裂、垫圈压缩后不回弹。而这两类问题里，由材料本身引起的比例并不高。环境应力开裂的判据在标准里写得很清楚：ASTM D1693 用弯条法在 50℃、10% Igepal CO-630 水溶液中记录 50% 试样开裂时间 F₅₀；ISO 22088-3 用恒拉伸应力法在 40℃ 介质中测断裂时间或临界应力；ISO 6252 用恒应变法（控制应变 1.0-2.0%、加速温度 50-80℃）。压缩永久变形则按 GB/T 7759.1 / ISO 815-1（常温高温）、GB/T 7759.2 / ISO 815-2（低温）测定。
行业通行的做法是把三件事一起定：选抗 ESC 的共聚 PP 基体、控制注塑内应力（模温、保压、浇口位置）、避免与强表面活性剂长期接触的设计。耐 ESC 的抓手不是"选一款更耐的料"这么简单，是这三件事同时做。 单看任何一项都没意义。
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）粒子里的耐 ESC 共聚方向与填充增强方向，按洁具的接触介质和浅色外观要求给到对应的基材档位与助剂体系；TPV 类弹性体可按密封件的压缩率与回弹要求配合选材。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：TPV 和"加软的 PP"是不是一回事？
答：不是。TPV 是 PP 连续相 + 交联 EPDM 分散相的两相体系，动态硫化做出来的，既有塑料的加工性又有橡胶的回弹。普通 PP 是刚性塑料，受压不回弹，做不了密封垫圈。看一个弹性体是不是 TPV，别只看硬度，要看它的两相结构和压缩永久变形表现。
问：垫圈只看硬度行不行？
答：不行。硬度只决定"压得动压不动"，压缩永久变形才决定"松开之后还能不能弹回来"——后者才是密封寿命的决定项。选型时硬度和压缩永久变形都要看，而且压缩永久变形必须带"温度 + 时间 + 压缩率 + 标准号"四个条件才有比较意义。
问：卫浴壳体加了抗菌剂，是不是就不会裂了？
答：不会。抗菌剂管的是浅色面的霉斑和细菌，开裂是环境应力开裂（ESC），根因是"应力 + 介质 + 时间"三要素同时在场。加了抗菌剂的浅色件照样会因 ESC 裂。两件要分别验证：抗菌按 GB/T 31402-2015，耐裂按 ASTM D1693 / ISO 22088-3。
问：能不能用普通填充 PP 直接做密封垫圈？
答：不能。普通填充 PP 是刚性件，没有交联橡胶相，受压后基本不回弹，不具备密封所需的弹性恢复。密封垫圈应走 TPV 这类热塑性硫化胶；普通 PP 适合壳体、支架这类刚性结构件，两者分工不同。
| 工况 | 关键判据 | 科隆常规供应 |
|---|
| 卫浴密封垫圈 | 压缩永久变形（70℃×22h）；低温回弹 | TPV 类弹性体选材配合（PP/EPDM 动态硫化方向） |
| 卫浴洁具壳体 | ESC 评价通过；浅色面不开裂 | 耐 ESC 抗冲共聚 PP + 矿物填充方向 |
| 免喷涂抗菌壳体 | 抗菌活性值；防霉等级 | 耐 ESC 共聚 PP + 无机抗菌剂方向 |
想提醒一句：件出问题，最常见的错法是先换料。压缩不回弹、壳体开裂、浅色面发白——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。
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。
Sealing gaskets and bathroom fixture housings are made of modified PP, and the two criteria most easily overlooked are compression set and detergent resistance (ESC). This article thoroughly explains the two-phase structure of TPV, provides the counterintuitive conclusion that the 'hardness of the gasket is not the determinant of service life,' and outlines the three key factors for environmental stress cracking of bathroom housings, along with the verification sequence and material substitution checklist.
The bathroom faucet housings we made have only been installed for half a year, and the light-colored surface has turned white and even developed a crack. Is it because the material is not durable?
The gasket was chosen with a hardness of 70A, but it started leaking after three months of installation. Isn't the hardness supposed to be enough? Why is it still leaking?
I have been asked these two questions many times back and forth. The people asking think they are two separate issues—one about cracking, the other about leaking—but the root cause actually points to the same blind spot in component selection: washers are chosen based on hardness and tensile strength, bathroom housings are chosen based on color and rigidity, and no one considers the main issue of 'whether it can still rebound after long-term compression' and 'whether it will crack after long-term exposure to cleaning agents'.
Next, break it down from four levels: working conditions, routes, criteria, and verification. First, let's discuss the most important structural knowledge point of this article.
1. Water leakage from the sealing gasket and whitening of the bathroom housing both originate from 'treating TPV as soft PP'.
First, let's correct a common misunderstanding: the sealing gasket material (TPV) is not "softened PP"; it is a two-phase system obtained by dynamically vulcanizing EPDM (dispersed phase) in polypropylene (continuous phase).
This point is the foundation for all the judgments in this article and must be explained thoroughly. The process of dynamic vulcanization is as follows: under high temperature and high shear, the EPDM rubber phase crosslinks into micron-sized particles, which are then evenly dispersed in the PP continuous phase. The result is that the PP continuous phase contributes plastic properties such as heat resistance, weather resistance, and injection-moldable recyclability, while the crosslinked EPDM dispersed phase contributes rubber elasticity and sealing performance. Therefore, it is neither as hard and brittle as pure PP, nor like traditional vulcanized rubber that can only be vulcanized and cannot be injection molded.
A judgment that peers cannot copy: The performance of TPV comes from the two variables of 'ratio of the two phases and degree of crosslinking,' not from 'how soft the PP is.' Even for TPVs labeled with the same 70A hardness, if the EPDM phase ratio is slightly lower and the PP phase ratio is slightly higher, the rebound performance after compression can be quite different—this is why two grades with the same hardness can have vastly different gasket lifespans. Choosing materials based solely on hardness is equivalent to looking at only one corner of the formulation.
The casing of sanitary ware takes a different path: it requires a rigid exterior, not elastic sealing parts. Therefore, the main material is impact-resistant copolymer modified PP, with mineral/talc fillers added if necessary to enhance rigidity and additives to improve resistance to cleaning agents. Later, it will be discussed that its main mode of failure is not rebound, but environmental stress cracking (ESC).
2. Six-Dimensional Analysis of Working Conditions: Gasket under long-term compression, sanitary ware soaked in cleaning agents for a long time, provide numbers for the six dimensions
Although washers and bathroom housings are both of the 'PP series,' their working conditions are completely different. Only when the six dimensions are aligned can the direction come out.
| Dimension | Actual operating conditions of the sealing gasket (TPV) | Actual working conditions of bathroom sanitary ware housing (modified PP) | Requirements for the materials |
|---|
| Temperature | Operating temperature 23-70℃; can be installed in winter down to −20~−30℃ | Long-term exposure to 40-60°C hot water, instantaneous 80-95°C near the mixing valve/shower head | Gaskets should be checked for low-temperature rebound; housings should be checked for heat resistance and thermal stress. |
| Load | Design compression ratio 15-25% (commonly 25% according to GB/T 7759) | Assembly preloading: Residual stress from injection molding needs to be controlled at a low level | Check the gasket for permanent compression deformation; check the housing for residual stress. |
| Medium | Engine oil/grease (bathroom hardware), water; partially exposed to mild detergents | Detergent/surfactant concentration is commonly 1-10%, strong alkaline toilet cleaner pH>12 | Check the volume change rate for the gasket; check ESC resistance for the housing. |
| Lifespan | Repeated compression 10,000-50,000 times without failure | The typical design lifespan is 5-10 years (approximately 1.8-3.6×10⁴ hours) | Check the washer for rebound retention; check the casing for long-term crack resistance |
| Appearance | Mostly dark-colored elastic parts, with low appearance requirements | For surfaces with frequently unpainted light-colored appearances, ΔE needs to be controlled | Light-colored surfaces are prohibited from cracking, mold spots, and color differences |
| Compliance | Drinking water/food contact materials must comply with GB 4806; recyclable | Antibacterial parts need GB/T 31402-2015; food grade needs GB 4806 | Set standards according to usage, do not mix |
Among the six dimensions, the veto criterion for the gasket is permanent compression deformation, and the veto criterion for the housing is ESC resistance—these two criteria have not been taken as the main focus in the trade edition and the existing home appliance section, and this article will focus on them.
A professional detail: The algorithm for the permanent compression deformation rate is CS = [(h₀ − h₁) / (h₀ − hₛ)] × 100%, where h₀ is the original thickness, h₁ is the thickness after recovery, and hₛ is the height of the limiter (compressed state). For the same batch of material, whether the compression rate is 25% or 30%, and whether the insulation time is 22 hours or 70 hours, the resulting numbers can differ greatly. Therefore, when discussing permanent compression deformation, if the four conditions "temperature, time, compression rate, standard number" are not reported, the number has no comparative significance.
3. Two parallel routes: gaskets go through TPV, bathroom housings use ESC-resistant copolymer PP
For the same 'PP system', the washers and the housing fall on two completely different paths. This is just a statement of division of labor, not judging which is better.
| Route | Material Form | Get what | The Price Paid / Boundaries |
|---|
| Sealing gasket materials (TPV, PP/EPDM dynamically vulcanized) | Two-phase system, PP continuous phase, crosslinked EPDM dispersed phase | Rubber rebound Suitable for injection molding recycling Weather-resistant and ozone-resistant | High temperature resistance upper limit is about 100-135°C (depending on the grade); poor resistance to aromatic solvents |
| Impact-resistant ESC copolymer PP (mineral/talc filled) | Homogeneous/Semi-homogeneous PP Impact-resistant copolymer Filled | Rigid appearance Resistant to cleaning agents Light-colored surface without spraying | It is a rigid part itself, without sealing rebound; relies on ESC evaluation for quality control. |
| Traditional vulcanized rubber (EPDM/NBR/FKM, used as a control) | Vulcanized crosslinked network | Dedicated media have stronger resistance (especially FKM solvent resistance, NBR oil resistance) | Cannot be injection molded, cannot be recycled, high cost, requires vulcanization process |
The classification is very straightforward: if you need rebound sealing, use TPV; if you want a rigid appearance and long-term exposure to cleaning agents, use ESC-resistant copolymer PP. The two are not substitutes; they represent the division of labor between the "moving parts" and "stationary parts" in the same bathroom component—the gasket is responsible for sealing, and the housing is responsible for support.
Dare to deny a common practice: some people use ordinary PP or even just any kind of filled PP as a sealing gasket for the sake of 'convenience.' This is wrong. Ordinary PP is a rigid plastic and does not have a cross-linked rubber phase. It basically does not rebound after being compressed and fundamentally lacks the elastic recovery needed for sealing—gaskets should be made from TPV or similar thermoplastic vulcanizates, not rigid PP.
4. ★ Selection Criteria Table: Compressive Permanent Deformation, ESC Resistance, each criterion comes with a verification method
The table below is the part of the entire article most worth saving. Pay attention to the fourth column "Verification Method · Standard Number" — when selecting, the part that most often gets stuck is not "which indicator to look at," but "what to measure it with, and how much counts as passing."
| Indicator | Threshold Value (Typical) | Verification Method · Standard Number | Common Failures | Common solution |
|---|
| Compression set (70℃ × 22h, 25% compression) | ≤25-30% (According to publicly available grade data, Grade B) | GB/T 7759.1-2015 / ISO 815-1:2019; ASTM D395-18 Method A (constant compression rate) | Insufficient rebound after release, leak in the sealing gap | Choose TPV with an appropriate degree of crosslinking and control the PP phase content |
| Low-temperature compression permanent deformation (−20~-30°C × 22h) | The lower the better, according to GB/T 7759.2-2019 / ISO 815-2:2019 | GB/T 7759.2-2019 / ISO 815-2:2019 | Does not spring back after winter installation, leaks when cold-installed | Increase the EPDM phase ratio and review the substrate grade |
| Volume change resistance to medium (after soaking) | The oil immersion expansion rate is approximately ≤8% (Grade B) according to public data; immersion in cleaner needs to be controlled. | GB/T 1690 / ISO 1817 GB/T 7759.1 Soaking Method | Swells and softens, extruded from the sealing groove | Control the PP phase ratio and select the grade resistant to the medium |
| Environmental Stress Cracking (ESC) (Sanitary Ware Housing) | Evaluation: ASTM D1693 50°C, 10% Igepal CO-630, the longer the F₅₀ time, the better; ISO 22088-3, the higher the critical stress, the better | ASTM D1693 (Bent Strip Method); ISO 22088-3 (Constant Tensile Stress Method, 40°C); ISO 6252 (Constant Strain Method, 1.0-2.0% Strain, 50-80°C) | The light-colored surface is whitening and cracking along areas of stress concentration | ESC-resistant copolymer PP Control injection molding internal stress |
| Hardness (Shore A) | Gasket 40-80 Shore A, reverse judged according to sealing force | GB/T 531.1 / ISO 7619-1 | Cannot be compressed or collapsed | Designed based on compressive strength, not just hardness |
| Antibacterial rate (light-colored bathroom surfaces) | Antibacterial activity value meets the standard according to the patch method | GB/T 31402-2015 / ISO 22196:2011 (film method, 24h); Antifungal ISO 16869:2008 / ASTM G21 | Light-colored surfaces develop mold spots, affecting appearance | Silver/Zinc Inorganic Antibacterial Agent Durability Verification |
Text version conclusion: Among the six lines, permanent compression deformation and ESC are the two items that should be looked at first—the former determines whether the gasket can still bounce back after being released, and the latter determines whether the casing will crack when soaked in detergent. Hardness and antibacterial properties are auxiliary criteria and should not dominate the evaluation. Treat this table like a medical check-up form; if one item is missing, do not consider it qualified. This saves much more money than installing it only to have leaks or cracks later.
5. Common Failures and Root Causes: Four Phenomena, Four Root Causes
Failure 1: The gasket is selected based on hardness, and it leaks within three months. The root cause is almost always "focusing on hardness, not on compression set." Hardness only determines "whether it can be compressed," while compression set determines "whether it bounces back after being released" — the latter is what actually determines the sealing life. This is a very common mistake in the industry: treating hardness as the sole criterion for selecting sealing materials.
Failure 2: The bathroom shell turns white and cracks after being soaked in a cleaning agent for a long time. The root cause is environmental stress cracking (ESC), which occurs only if three factors are present simultaneously: stress (assembly internal stress, injection molding residual stress), medium (detergents, surfactants, soapy water), and time. If any one is missing, cracking will not occur. The mechanism recorded in public sources is that surfactants, in combination with stress, induce silver streak propagation, eventually leading to cracking (according to technical information from public testing institutions, Level B).
Failure 3: The gasket swells in volume after being exposed to the medium and is extruded from the sealing groove. The root cause is that the PP continuous phase is swollen by oils/solvents. In TPV, the higher the PP phase proportion, the worse the resistance to mineral oil and aromatics. For grades with the same hardness but different EPDM/PP ratios, oil resistance can differ by one level.
Failure Four: Light-colored shells that are spray-free both crack and have color differences. The attribution needs to be divided into two steps: for cracking, first look at ESC and residual stress; for color difference, first look at the color masterbatch and the batch. Antibacterial agents deal with mold spots, not cracking — light-colored parts with antibacterial agents can still crack because of ESC. These two issues should not be confused.
6. Verification sequence: what is a priori, what is a posteriori
Almost no one in the industry writes this part, but it is the key to whether material changes can save money. If the order is wrong, the costs will concentrate and explode at the final step.
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① Sample Physical Comparison Hardness / Tensile / Elongation at Break / Bulk Density
↓ The basic items are within the threshold before proceeding.
② Compression permanent deformation TPV gasket: 70℃ × 22h (25% compression) first test
If you don't pass this level, you don't need to do the rest.
③ ESC Evaluation Bathroom Shell: ASTM D1693 / ISO 22088-3 / ISO 6252
↓ Critical stress/cracking time does not meet the standard, return for material selection
④ Low-temperature rebound verification −20~-30°C × 22h Compressive permanent deformation (GB/T 7759.2)
↓ Winter installation parts must pass
⑤ Short-shot mold trial Check filling, weld lines, internal stress distribution, and appearance of light-colored surfaces
↓ Only after the short test run succeeds can we talk about mass production
⑥ Batch Trial Production Client-side Verification
`
Each step has a clear criterion of 'just go back to the previous level.' The most common mistake is skipping steps ② and ③ and going straight to ⑤, using test molds to judge material performance—the molding conditions of the test molds are often temporary, the measured numbers are not representative, and only when installed on-site do you find leaks or cracks, by which time the loss is already for the entire batch.
Text version conclusion: The verification sequence is sample → compressed permanent deformation → ESC → low-temperature rebound → short shooting → batch. The compressed permanent deformation and ESC steps must be completed before mold testing because they are the most likely items to result in outright rejection; only after passing these should mold-related work be done, so as not to waste the cost of mold testing.
7. Reverse honesty: In these three situations, this part should not use modified PP (TPV is also insufficient)
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 is modified PP/TPV not suitable? | Which way should I go? |
|---|
| Requires long-term exposure to strong solvents or high concentrations of strong surfactants (such as aromatics, chlorinated solvents, or continuous soaking in high-concentration strong bases) | PP has limited resistance to this type of medium when in continuous contact, and volume changes and swelling are difficult to control. | Fluororubber FKM (solvent-resistant), Nitrile Rubber NBR (oil-resistant), or special corrosion-resistant elastomers |
| Requires long-term high-temperature sealing (continuously above 100℃, even normally above 135℃) | The temperature limit of TPV is approximately 100-135°C (depending on the grade), and continuous overheating will accelerate permanent deformation and aging. | Silicone rubber (wider temperature resistance) or fluorine rubber FKM |
| Requires extremely high compression rebound accuracy (such as precision hydraulic seals, high-pressure dynamic seals) | The compression set and stress relaxation accuracy of TPV do not reach the level required for precision hydraulic seals. | Nitrile rubber (NBR), fluororubber (FKM), or specialized hydraulic sealing elastomer |
The pattern is very clear: whenever any of 'medium strength, temperature, or rebound precision' reaches the PP system boundary, it indicates that this seal should not use modified PP (including TPV) for rigid support. When encountering such a requirement, our approach is to first clarify this point before discussing any compromise — for orders that proceed rigidly, they ultimately have to be returned through rework and claims.
8. What to Move When Changing Materials: A Checklist to Review Before Taking Action
Before deciding to try modified PP (or to switch the existing material to TPV/ESC-resistant copolymer PP), it is recommended to go through this table first. The customer's real concern is often not performance, but 'Do 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 shrinkage rates of TPV and rigid PP are different, so the dimensions of the sealing groove/housing need to be checked. | Dimensions are out of tolerance, assembly does not fit, or sealing groove is too tight |
| Gate and Venting | TPV has different flow and elastic recovery characteristics, and the position of the case gate affects internal stress | Insufficient filling and residual stress concentration lead to ESC |
| Material Temperature and Mold Temperature | TPV injection molding 175-210°C (according to publicly available grade information, Class B); the mold temperature of the housing affects internal stress | Surface defects, excessive internal stress, increased ESC risk |
| Dry | Most TPVs do not require drying (optional 80°C × 3h); the housing is determined according to the system | Silver threads, bubbles, light-colored surface defects |
| Pressure Holding and Demolding | The demolding logic of elastomer rebound is the opposite of rigid parts | Deformation, ejection tearing, elastic part sticking to the mold |
| Color difference | For paint-free light-colored housings, the color swatch must be confirmed before going on the machine. | Batch color difference disputes, light-colored surface appearance not meeting standards |
| Verification order | Sample → Compressive Permanent Deformation / ESC → Short Shot → Batch | All the risks are concentrated to explode at the final step |
Text Version Conclusion: Changing materials involves molds, processes, and color differences, among which the verification sequence should be discussed first. Skipping small samples and going straight to mold testing is equivalent to spending the cost in advance; skipping ESC/permanent compression deformation testing and going directly to mass production means that a single failure could result in recall-level losses for the entire batch.
9. One-page report sheet (can be directly pasted into PPT)
| Scene | Recommended Route | Key indicators | Verification Standard | Conditions that need to be confirmed first |
|---|
| Construction/Bathroom Sealing Gasket | TPV (PP/EPDM Dynamically Vulcanized) | Compression set ≤25-30% (70°C × 22h); low-temperature rebound meets the standard | GB/T 7759.1 / ISO 815-1; GB/T 7759.2 / ISO 815-2 | Operating temperature, compression ratio, contact medium |
| Sanitary ware casing (light color, no spray coating) | ESC-resistant impact copolymer PP mineral filled | ESC passes the evaluation; the light-colored surface does not crack, and ΔE is controlled | ASTM D1693 / ISO 22088-3 / ISO 6252; GB/T 531.1 | Type and concentration of cleaning agents, assembly stress |
| Paint-free antibacterial casing | ESC-resistant copolymer PP Inorganic antibacterial agent | Antibacterial activity value meets the standard; mold resistance level | GB/T 31402-2015 / ISO 22196; ISO 16869 | Simultaneous acceptance of antibacterial and ESC dual indicators |
| Winter Installation/Low-Temperature Condition Gasket | TPV (high EPDM phase proportion) | Low-temperature compression permanent deformation meets the standard | GB/T 7759.2 / ISO 815-2 | Record of the lowest local temperature |
Text version conclusion: The purpose of this table is to allow technicians to report conclusions directly without having to reorganize their wording. There is only one criterion for judgment—whether the client can use this table to finalize the direction of the materials in one meeting.
10. The part of this item that is most prone to problems is often not the material.
One of the most common types of early failures in the sanitary ware and sealing components industry is the whitening and cracking of housings after prolonged contact with cleaning agents, and the inability of gaskets to rebound after compression. However, in these two types of problems, the proportion caused by the material itself is not high. The criteria for environmental stress cracking are clearly stated in the standards: ASTM D1693 records the time for 50% of specimens to crack (F₅₀) in a 50°C, 10% Igepal CO-630 aqueous solution using the bent strip method; ISO 22088-3 measures the time to fracture or critical stress under constant tensile stress in a medium at 40°C; ISO 6252 uses the constant strain method (controlling strain at 1.0-2.0%, accelerated temperature 50-80°C). Compression set is measured according to GB/T 7759.1 / ISO 815-1 (normal and high temperature) and GB/T 7759.2 / ISO 815-2 (low temperature).
The industry's common approach is to set three things together: selecting ESC-resistant copolymer PP substrates, controlling internal stress in injection molding (mold temperature, holding pressure, gate position), and avoiding long-term contact with strong surfactants. The key to ESC resistance is not simply "choosing a more durable material"; it requires doing all three at once. Focusing on just any one is meaningless.
Ningbo Kelong New Materials Co., Ltd. commonly supplies ESC resistance copolymer directions and filling enhancement directions in modified polypropylene (PP) pellets for this part, providing corresponding substrate grades and additive systems according to the contact medium and light-colored appearance requirements of the fixture; TPV elastomers can be selected according to the compression ratio and rebound requirements of the seal. Formulations can be adjusted according to the working conditions of the parts, allowing for sample comparison and mold trials, and can accommodate multi-variety, small-batch customer demands.
FAQs
Question: Are TPV and "softened PP" the same thing?
Answer: No. TPV is a two-phase system of continuous PP + cross-linked EPDM dispersed phase, produced by dynamic vulcanization. It combines the workability of plastic with the springback of rubber. Ordinary PP is a rigid plastic that does not bounce back under pressure, so it cannot be used to make sealing gaskets. To determine if an elastomer is TPV, don't just look at hardness; look at its two-phase structure and performance of permanent compression deformation.
Question: Is it okay to look only at hardness for washers?
Answer: No. Hardness only determines whether it can be pressed or not; compression permanent deformation determines whether it can bounce back after release—the latter is the key factor determining seal life. When selecting, both hardness and compression permanent deformation must be considered, and compression permanent deformation must meet four criteria: temperature + time + compression ratio + standard number to be meaningful.
Question: If a bathroom enclosure is treated with antibacterial agents, will it not crack?
Answer: No. Antibacterial agents control mildew and bacteria on light-colored surfaces; cracking is environmental stress cracking (ESC), and the root cause is the simultaneous presence of "stress + medium + time". Light-colored parts with antibacterial agents will still crack due to ESC. Both parts need to be verified separately: antibacterial according to GB/T 31402-2015, crack resistance according to ASTM D1693 / ISO 22088-3.
Question: Can ordinary filled PP be used directly to make sealing gaskets?
Answer: No. Ordinary filled PP is a rigid component without cross-linked rubber phases, and it basically does not rebound under pressure and does not have the elastic recovery needed for sealing. Sealing gaskets should use thermoplastic vulcanized adhesives like TPV; Ordinary PP is suitable for rigid structural parts like housings and brackets, but the two have different roles.
| Operating Condition | Key Criteria | Cologne Conventional Supply |
|---|
| Sanitary Sealing Gasket | Compression Permanent Deformation (70°C×22h); Low-temperature rebound | TPV elastomer material selection (PP/EPDM dynamic vulcanization direction) |
| Sanitary ware housing | ESC Evaluation passed; Light-colored surface does not crack | ESC-resistant impact-resistant copolymer PP + mineral filling direction |
| Spray-free antibacterial shell | Antibacterial activity value; Anti-mold rating | ESC-resistant copolymer PP + inorganic antibacterial agent direction |
Just a reminder: when parts have problems, the most common mistake is to change the material first. No rebound when compressed, shell cracking, light-colored surfaces turning white—each has more than one cause. Position first, then change the material; If the order is reversed, you often end up in the same place after several rounds of replacement.
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The most common mistake when parts have problems is to change the material first.
Low-temperature brittle cracking, warping, cracking, strong odor—each has more than one cause. It could be the wrong base material position, the molding conditions not keeping up, or it could indeed be a material issue. Position first, then change the material; If the order is reversed, it often ends up stuck in place after several rounds of replacement.
Ningbo Kelong New Materials Co., Ltd. produces modified polypropylene (PP) pelletizing and covers three levels of substrates: homopolymer, random copolymer, and impact-resistant copolymer, as well as modification directions such as filling, glass fiber reinforcement, toughening, flame retardancy, low odor and low VOC, weather resistance, and no coating or scratch resistance; Also engaged in PP resin, sub-brand materials, and large package materials for major petrochemical plants
