低压线缆护套用什么料？无卤阻燃改性PP 能做到 V-0 与无卤，但 25-30% 的阻燃加量会把柔韧压下去——阻燃和耐弯折，是一对绕不过的敌人。这篇把三条补法的代价、十项判据与验证顺序摆清楚，也讲清哪四类线缆不该用它。
"护套料 V-0 是过了，可客户装上去半年，弯折的地方开始发白开裂。"
问话的人做低压控制电缆，原来护套走含卤体系，为满足无卤与 RoHS 换成了无卤阻燃改性PP——阻燃那关顺利过了，柔韧这关塌了。
现场现象四条：盘好的线缆放开后弯曲半径最小的几处起白纹；冬天户外放线一掰就崩口；装上半年护套变硬，再弯就裂；长段直敷那批接头处露出芯线。
四条指向同一件事：低压线缆护套用无卤阻燃改性PP，阻燃和柔韧是一对敌人，谁也绕不过。
最硬的数先摆出来：无卤阻燃体系在 PP 里的典型加量在 25-30%（公开资料口径）。这么多刚性无机粒子进基体，断裂伸长率和低温冲击必然往下掉。你要的是 V-0，付出去的是柔韧。
所以本篇要回答的不是"能不能同时做到"，而是"用哪一条补、这笔代价能不能接受"。
一、工况六维拆解：低压线缆护套的温度与载荷两项，是一票否决的
低压线缆护套的六维工况里，温度和载荷最该先看——护套的两类致命失效都出在这两维。
| 维度 | 实际工况 | 对材料的要求 |
|---|
| 温度 | 机柜与桥架内长期 70-90℃（导体发热叠加），耐温等级常见 70 / 90 / 105℃；户外低温 −25℃ 乃至 −40℃ 级 | 长期耐温与低温柔韧，两项都要 |
| 载荷 | 敷设牵引、安装弯曲半径、盘绕与反复弯折；固定敷设与移动敷设是两个世界 | 断裂伸长率与抗弯折，不是刚性 |
| 介质 | 矿物油（IRM902 口径）、UV、臭氧、清洗剂与潮气 | 耐油、耐候、耐臭氧、耐潮湿 |
| 寿命 | 设计要求常见 20-30 年；长期通电升温叠加老化 | 老化后的柔韧保持率 |
| 外观 | 印字与色标（线规、温度等级、厂标）；表面无裂纹、无粉化、耐刮磨 | 印字耐磨、色差稳定 |
| 合规 | 单根垂直燃烧、无卤、低烟、RoHS | 阻燃档位与无卤口径 |
文字版结论：温度和载荷这两维最该先看。低温安装崩口是温度问题，反复弯折开裂是载荷问题。"耐温多少、最低弯到多少度、弯几次"三个数报齐，方向基本就出来了。
二、材料路线分工：无卤阻燃改性PP护套、交联聚烯烃、TPE/TPU 与 PVC 各管一段
先给结论：无卤阻燃改性PP 不是"更好的护套料"，它是四条路线里密度低、成本低、可回收的那一条，主场在户内固定敷设的低压线缆上。
但这条路线有一个绕不过去的机制。
2.1 阻燃剂加 25-30%，柔韧为什么必然掉
加量要堆到这一档，是 PP 的结构特点决定的——它极限氧指数本来只有 17.5 左右。而堆进去的是刚性无机粒子，不是柔性链段，后果有两条：
- 断裂伸长率与低温冲击急剧下降，护套变硬、变脆；
- 阻燃剂颗粒本身可能成为应力集中点，成为开裂的起点。
第二条最容易漏。护套开裂的位置往往不是壁厚最薄处，而是分散不均、有团聚粒子的地方。在现场它就是两件事：反复弯折时护套开裂，低温安装时崩口。
2.2 三条补法，三笔代价
| 补法 | 拿到什么 | 代价 |
|---|
| ① 增韧（POE / EPDM） | 断裂伸长率与低温冲击补回来 | 可燃橡胶相进入基体，拉低阻燃效率；仍要过 V-0 就得再加阻燃剂，加量上去又把刚补的柔韧推下去 |
| ② 换效率更高的阻燃体系（如某些磷氮膨胀体系） | 同一档位下加量可以压下来 | 成本上升、加工窗口收窄（阻燃剂分解温度必须匹配加工温度），部分体系吸潮明显 |
| ③ 双层共挤（内层柔、外层阻燃） | 柔韧与阻燃分开承担 | 工艺复杂度上升，多一层界面要控，壁厚与偏芯更难压 |
核心判断就一句：这三条没有免费的。 要问的不是"能不能同时做到"，而是"用哪一条补、代价能不能接受"。
敢否定一个常见做法：很多项目是"先按 V-0 选料，再想办法补柔韧"。顺序反了。该先定的是柔韧的底线——最低安装温度、最小弯曲半径、弯折次数。阻燃档位是安规给的，是死的；柔韧底线是设计和安装方式给的，是活的。
2.3 四条路线，各管一段
| 路线 | 代价 / 边界 | 适配段 |
|---|
| 无卤阻燃改性PP护套 | 密度低、成本低、可回收；柔韧上限受限，长期 90℃ 以上受窗口限制 | 户内固定敷设的低压线缆、控制电缆 |
| 交联聚烯烃（XLPO） | 耐温、耐候、电性能稳；但热固不可回收、修复难 | 无卤低烟主干、耐温要求更高的段落 |
| 热塑弹性体（TPE / TPU） | 柔顺、低温好、耐磨好；成本偏高，耐油与耐温窗口看体系 | 频繁移动、拖链、卷筒等柔性电缆 |
| PVC | 成本低、柔软度与加工成熟度高；含卤，燃烧释放卤化氢与浓烟 | 无无卤要求的常规低压线缆 |
文字版结论：四条不是替代关系，是分工关系。要求无卤低烟、预算可控、敷设方式固定，那是无卤阻燃改性PP 的主场；要求极柔、频繁移动，或长期 90℃ 以上，或烟密度要求极严，就该往 XLPO、TPE/TPU 走。PVC 含卤燃烧产烟要交代清楚（公开资料口径：含卤体系卤酸气体释放量 15-40 mg/g 量级，无卤按 ≤5 mg/g 判），但它在成本与柔软度上仍占着自己的一段——这是分工问题，不是谁好谁坏的问题。
三、★ 低压线缆护套选型判据表：十项指标，每项都带验证方法与标准号
选型最常卡住的不是"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 |
|---|
| 单根垂直燃烧 | 单根垂直蔓延通过；成束敷设另按成束要求 | GB/T 18380.12（等同 IEC 60332-1-2） | 护套助燃、火焰沿缆蔓延 | 加量上调，或换效率更高的体系 |
| 无卤 + 低烟 | 卤酸气体（HCl 计）≤5 mg/g；pH ≥4.3；电导率 ≤10 μS/mm；透光率 ≥60%；溴 <900 ppm、氯 <900 ppm、总和 <1500 ppm | GB/T 17650.1、GB/T 17650.2；烟密度 GB/T 17651.2 | 腐蚀性气体、烟密度超标 | 无卤体系 + 低烟填料，不加含卤助剂 |
| 灼热丝（整机有要求时） | GWIT 750 / 775℃；GWFI 850 / 960℃；850℃ 灼热丝接触 30 s 不引燃 | GB/T 5169.13（GWIT）、GB/T 5169.12（GWFI） | 灼热丝起燃、滴落引燃 | 提高成炭与阻燃效率 |
| 断裂伸长率（原始） | 无卤阻燃聚烯烃护套料常见 150-250%（B 级）；护套门限常见 ≥150% | GB/T 2951.11 | 弯折处起白纹、开裂 | 增韧，或压低阻燃加量 |
| 老化后断裂伸长率保持率 | 100℃×168 h 后变化率 ≤±30% | GB/T 2951.12 | 新料能弯，老化后弯不动、发脆 | 抗氧体系 + 低吸潮阻燃体系 |
| 低温卷绕 / 低温拉伸 | −15 / −25 / −40℃ 按件定；低温拉伸伸长率 ≥30% | GB/T 2951.14 | 低温安装崩口、脆裂 | 抗冲共聚 + 增韧，或换高柔体系 |
| 热收缩 | 收缩率 ≤3%（80℃ 档按标准可放宽） | GB/T 2951.13 | 长段直敷回缩、接头露芯 | 调结晶与冷却，复核收缩率 |
| 高温压力（热变形） | 80-90℃ 压痕深度 ≤50% | GB/T 2951.31 | 高温受压变形、护套压穿 | 提高耐温档 + 控填料比例 |
| 耐矿物油 / 耐化学 | IRM902，100℃×24 h 或 168 h；变化率常见 ≤±40% | GB/T 2951.21 | 油污环境溶胀、发软 | 选耐油基体与体系 |
| 体积电阻率 / 绝缘电阻 | 按产品标准与客户门限确认；成品另测芯线对护套绝缘电阻 | GB/T 31838.2（等同 IEC 62631-3-1） | 受潮后绝缘下降、耐压不过 | 高纯低离子体系 + 防潮干燥 |
文字版结论：十项里有两项最该先看——老化后断裂伸长率保持率，和低温卷绕 / 低温拉伸。前者决定护套能不能活过设计寿命，后者决定它能不能装上机。只测原始断裂伸长率的选型是不完整的：护套失效几乎都出现在服役几年之后。
还有一条得配套看：无卤阻燃体系（尤其膨胀型）容易吸潮，吸潮直接拉低电性能（B 级行业资料：无卤阻燃电缆料浸水一天后，体积电阻率可下降 60-80%）。这类护套上，干燥、包装、仓储都不是小事。
四、常见失效与根因：护套开裂、老化变脆、低温崩口、回缩露芯
四条现象、四条根因，归因顺序别搞反——搞反了，钱就花错地方。
失效一 · 弯折处起白、开裂（新料就出现）。 根因多半不是"料脆"，是断裂伸长率不够用。原始伸长率卡在 150% 附近，安装弯曲半径却按柔性电缆要求，就必然开裂。先看弯曲半径和安装方式，再看料。
失效二 · 新料能弯，老化后弯不动。 根因是热氧老化叠加阻燃体系吸潮与水解，伸长率保留率掉出 ±30% 那一档。验证项是 GB/T 2951.12 的老化后断裂伸长率，不是原始值——不少项目只测原始值就放行，装上去两年才暴露。
失效三 · 低温安装崩口。 根因是低温卷绕或低温拉伸不过。PP 在低温区本就接近脆化，加上 25-30% 的刚性粒子，是双重的短板。这一关要在小样阶段就用 −15 / −25 / −40℃ 卷绕或拉伸测出来。
失效四 · 护套回缩露芯、印字磨掉。 根因在热收缩与表面耐磨。换料后结晶行为变了，收缩也跟着变；耐刮磨多用刮针法（B 级行业资料口径），与表面硬度和印字工艺都相关。
敢否定第二个常见做法：有人靠"阻燃剂再多加两三份"来稳过 V-0。这是错的。加量再上去，柔韧继续掉、吸潮更重、绝缘电阻更低——拿 V-0 的余量去换柔韧、电性能和寿命，是一笔明显不划算的买卖。
五、验证顺序：低压线缆护套换料，先定安规、再定阻燃、再筛柔韧
这一段同行几乎不写，但它决定钱花在哪一步、以及最后会不会集中爆掉。
`
① 定整机安规要求 阻燃档位 / 无卤 / 烟密度 / 耐温等级 / 认证口径
↓ 这一级没定清，后面全部白做
② 定阻燃档位与体系 单根垂直燃烧（GB/T 18380.12）先过
↓ 过不去，退回 ① 确认档位是否定高了
③ 筛柔韧 断裂伸长率（GB/T 2951.11）+ 低温卷绕/拉伸（GB/T 2951.14）
↓ 不过，退回 ② 换体系或调加量
④ 验老化后柔韧保持率 100℃×168 h 后伸长率变化率 ≤±30%（GB/T 2951.12）
↓ 不够，退回 ②③ 重配体系
⑤ 电气复测 体积电阻率（GB/T 31838.2）+ 成品绝缘电阻；建议加湿态复测
↓ 受潮掉得多，退回 ② 换低吸潮体系
⑥ 整机布线验证 弯曲半径、敷设牵引、印字与色标、端子压接
`
最常见的错误是跳过 ③ 和 ④ 直接进 ⑥。 拿成品线缆判断材料柔韧，代价太高；跳过老化后保持率，等于把最大的风险留到两年后结算。
文字版结论：顺序是 安规 → 阻燃 → 柔韧 → 老化保持 → 电气 → 布线。柔韧和老化保持这两关必须在小样阶段过掉——它们最可能一票否决，也是此时改体系成本最低的两项。
六、反向诚实：这四类低压线缆护套，无卤阻燃改性PP不该当首选
先讲不该用的情况。下面这四类件，换路线比硬撑省钱。
| 出现的情况 | 为什么无卤阻燃改性PP不合适 | 该往哪走 |
|---|
| 长期使用温度要求 90℃ 以上 | PP 基体耐温窗口就在这条线附近，靠填充往上抬有边界 | 交联聚烯烃（XLPO）或更高耐温体系 |
| 要求极高柔韧（频繁移动的柔性电缆、拖链、卷筒电缆） | 柔韧与阻燃的对拉消不掉，PP 基很难把高柔与高阻燃同时给足 | TPE / TPU，或高柔 XLPO |
| 要求极低烟密度与无毒（人员密集与隧道场景） | PP 基体系在极低烟密度这一档上很难同时满足 | 无卤低烟聚烯烃（XLPO）体系 |
| 要求长期浸油、强溶剂或强极性介质 | 介质对该基体的侵蚀是体系性的，配方兜不住 | 按介质选耐蚀弹性体体系 |
规律是一致的：凡是"两个方向相反的要求同时要、而且都要给足余量"，就该换路线，不该用 PP 硬撑。 遇到这种需求，我们的做法是先把这条讲清楚，再谈有没有折中空间——硬接下来的单子，最后都要用返工和索赔还回去。
七、换料要动什么：护套挤出线上先看再动的清单
客户决定试无卤阻燃改性PP护套之前，这张表建议先过一遍。
| 要动的项 | 需要确认什么 | 不做会怎样 |
|---|
| 挤出温度分布 | 阻燃体系熔体粘度偏高，机筒与口模温度要上调，但受阻燃剂分解温度限制 | 表面粗糙、气孔、阻燃剂分解析出 |
| 螺杆与剪切 | 阻燃粒子在高剪切下易破碎、分散不均 | 表面麻点、指标批次波动 |
| 干燥与包装 | 无卤阻燃体系吸潮明显，需确认干燥条件与包装方式 | 气泡、银纹，绝缘电阻下降 |
| 口模与拉伸比 | 熔体强度不同，拉伸比要重新定 | 护套偏芯、壁厚不均 |
| 冷却与牵引 | 结晶行为与收缩率都变了 | 护套回缩、露芯、尺寸超差 |
| 色差与印字 | 色母与阻燃体系相互作用；印字附着需重验 | 批次色差、印字耐磨不过 |
| 验证顺序 | 安规 → 阻燃 → 柔韧 → 老化保持 → 电气 → 布线 | 风险全压到最后一步集中爆发 |
文字版结论：换料要动的是温度、螺杆、干燥、口模、冷却五块工艺，加色差与印字两块验收。其中最该先谈的还是验证顺序——先在小样上把柔韧和老化保持过掉，再动挤出参数。
八、一页纸汇报表：低压线缆护套选材结论直接贴进 PPT
这张表的作用是让技术员把结论直接往上报，不必重新组织语言。
| 场景 | 推荐路线 | 关键指标 | 验证标准 | 需先确认的条件 |
|---|
| 户内固定敷设低压控制线缆 | 无卤阻燃改性PP + 增韧体系 | 单根垂直燃烧、断裂伸长率、老化后保持率 | GB/T 18380.12、GB/T 2951.11、GB/T 2951.12 | 阻燃档位、耐温等级、最小弯曲半径 |
| 户外或机柜间走线 | 无卤阻燃改性PP + 耐候体系 | UV 老化不劣化、低温卷绕、无卤低烟 | GB/T 16422.2、GB/T 2951.14、GB/T 17650.1/.2 | 最低环境温度、UV 暴露等级 |
| 北方低温安装环境 | 增韧加量上调，或改高柔体系 | −25 / −40℃ 低温卷绕或拉伸 ≥30% | GB/T 2951.14 | 安装期最低温度、施工方式 |
| 长段直敷、接头余量紧 | 调结晶与冷却，复核收缩率 | 热收缩率 ≤3% | GB/T 2951.13 | 敷设方式、接头预留长度 |
| 高柔、频繁移动 | 该走 TPE/TPU 或高柔 XLPO（不在本条路线） | 弯曲疲劳后不开裂 | 弯曲疲劳按 IEC 60811-504 / JB/T 10491 思路 | 弯折循环次数、最小弯曲半径 |
文字版结论：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。
九、低压线缆护套上最容易出问题的，往往不是阻燃没过
护套最常见的两类投诉是弯折开裂和老化后变脆，而这两类问题里，由阻燃等级不够引起的比例并不高。
阻燃那一关是明面上的门，判据清楚：单根垂直燃烧按 GB/T 18380.12，无卤按 GB/T 17650.1 / GB/T 17650.2。柔韧这一关是暗面上的门，很多项目在选料时根本没量化过——没定最低安装温度，没定最小弯曲半径，也没定老化后的保持率目标。
行业通行的做法是把四件事一起定：基材档位、增韧体系加量、阻燃体系选型（它决定加量能压到多少）、老化后的保持率目标。四者的配平关系才是这类件真正的技术难点。
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）粒子里的无卤阻燃 + 增韧方向，按件的阻燃档位、最低安装温度和弯曲半径给基材档位与阻燃体系，主要用来解决上面说的"阻燃过了、柔韧塌了"这一类问题；配方按件的工况调，可以配合做小样比对与老化后柔韧保持率验证，件级客户多品种小批量的需求也能接。
常见问答
问：无卤阻燃 PP 护套，V-0 和柔韧能不能一起做到？
答：能，但要付代价。增韧拉低阻燃效率，换体系增加成本并收窄加工窗口，双层共挤抬高工艺复杂度。问题不是"能不能"，是"用哪一条补、代价能不能接受"。
问：你们的无卤阻燃 PP 护套料，断裂伸长率能做到多少？
答：按件给，不给单个数。你需要给我的门限是三项：原始断裂伸长率、老化后保留率、低温卷绕温度。我们按这三项定体系，同时给原始值和老化后保留值——只给原始值的那份数据，用在护套上是不完整的。
问：为什么我们现在的料，新的时候能弯，装上去一年就脆了？
答：这是护套最典型的一条失效——老化后柔韧保持率。要查两件事：GB/T 2951.12（100℃×168 h）老化后断裂伸长率变化率有没有出 ±30% 那一档；阻燃体系是不是吸潮偏重。这两件事都在料和包装里，不在机台上。
想提醒一句：件出问题，最常见的错法是先换料。弯折开裂、老化变脆、低温崩口、回缩露芯——每一条的原因都不止一个。先定位，再换料；顺序反了，往往换了几轮还在原地。
最后说三句
低压线缆护套用无卤阻燃改性PP，阻燃和柔韧是一对敌人，谁也绕不过。 这不取决于配方水平，取决于 25-30% 这个阻燃加量。
要问的不是"能不能同时做到"，是"用哪一条补、代价能不能接受"。 增韧、换体系、双层共挤，三条路都有账要算。
验证顺序比验证项更重要。 安规 → 阻燃 → 柔韧 → 老化保持 → 电气 → 布线；柔韧和老化保持必须在小样阶段过掉。
关于我们
同一个牌号，两家做出来不一样，问题出在哪？
料是同一个料，工艺是两套工艺。干燥、挤出温度、螺杆组合、口模与冷却，任意一项偏了，出来就是两条不一样的线。选料选对了只算赢了一半。
宁波市科隆新材料有限公司，自产改性聚丙烯（PP）造粒，覆盖均聚 / 无规共聚 / 抗冲共聚三档基材，以及填充、玻纤增强、增韧、阻燃、低气味低 VOC、耐候、免喷涂耐划伤等改性方向；兼营各大石化厂 PP 树脂、副牌料与大包料。
What material is used for low-voltage cable sheaths? Halogen-free flame-retardant modified PP can achieve V-0 and be halogen-free, but a 25-30% increase in flame retardant will reduce flexibility — flame retardancy and bending resistance are an unavoidable pair of adversaries. This article clarifies the costs of three supplement methods, ten criteria, and the order of verification, and also explains which four types of cables should not use it.
"The jacket material V-0 passed, but after the customer installed it for half a year, the bent parts started to turn white and crack."
The person asking the question makes low-voltage control cables. Originally, the sheaths used a halogen-containing system. To meet halogen-free and RoHS requirements, they were changed to halogen-free flame-retardant modified PP—the flame-retardant requirement was passed successfully, but the flexibility requirement failed.
Four on-site phenomena: After coiled cables are released, the areas with the smallest bending radius show white marks; in winter, when laying cables outdoors, they break at a bend; after six months of installation, the sheath hardens and cracks when bent; for long straight runs, the joints in that batch expose the core wires.
All four point to the same thing: low-voltage cable sheaths use halogen-free flame-retardant modified PP; flame retardancy and flexibility are a pair of enemies, and neither can be bypassed.
Let's put the hardest numbers out first: the typical addition of halogen-free flame retardant systems in PP is 25-30% (according to public data). With so many rigid inorganic particles in the matrix, the elongation at break and low-temperature impact will inevitably decrease. What you get is V-0, but what you pay for is flexibility.
So what this article aims to answer is not 'whether it can be done at the same time,' but 'which solution to use, and whether the cost of this choice is acceptable.'
1. Analysis of six-dimensional operating conditions: The temperature and load of low-voltage cable sheaths are both veto items.
In the six-dimensional working conditions of low-voltage cable sheaths, temperature and load should be checked first—the two fatal types of sheath failure occur in these two dimensions.
| Dimension | Actual operating conditions | Requirements for the materials |
|---|
| Temperature | Cabinets and cable trays have long-term temperatures of 70-90°C (with conductor heating included), with common temperature ratings of 70 / 90 / 105°C; outdoor low temperatures range from −25°C to even −40°C. | Long-term heat resistance and low-temperature flexibility, both are needed |
| Load | Laying traction, installing bend radius, coiling and repeated bending; fixed laying and mobile laying are two different worlds | Elongation at break and bending resistance, not rigidity |
| Medium | Mineral oil (IRM902 caliber), UV, ozone, cleaning agents, and moisture | Oil-resistant, weather-resistant, ozone-resistant, moisture-resistant |
| Lifespan | Design life commonly 20-30 years; long-term energized heating combined with aging | Retention of flexibility after aging |
| Appearance | Printing and color coding (line gauge, temperature rating, manufacturer mark); surface free of cracks, no chalking, scratch-resistant | Print is wear-resistant and color difference is stable |
| Compliance | Single vertical burning, halogen-free, low smoke, RoHS | Flame-retardant grade and halogen-free caliber |
Text version of the conclusion: The two dimensions of temperature and load should be looked at first. Chipping during installation at low temperatures is a temperature issue, while cracking from repeated bending is a load issue. Once the three numbers 'how heat-resistant, minimum bending angle, number of bends' are reported, the direction will basically become clear.
2. Division of Material Routes: Halogen-free flame-retardant modified PP sheath, cross-linked polyolefin, TPE/TPU, and PVC each with one section of pipe
Conclusion first: Halogen-free flame-retardant modified PP is not a 'better sheath material.' Among the four routes, it is the one with low density, low cost, and recyclability, mainly used in low-voltage cables fixed indoors.
But this route has a mechanism that cannot be bypassed.
2.1 Flame retardant is added at 25-30%, why flexibility inevitably decreases
The dosage needs to be increased to this level, which is determined by the structural characteristics of PP — its limiting oxygen index is originally only around 17.5. And what is added are rigid inorganic particles, not flexible chain segments. There are two consequences:
- The elongation at break and low-temperature impact sharply decrease, and the sheath becomes hard and brittle;
- Flame retardant particles themselves may become stress concentration points and act as the starting points for cracking.
Article 2 is the easiest to miss. The cracks in the sheath often do not occur at the thinnest part of the wall, but in areas where the dispersion is uneven and there are agglomerated particles. On site, it manifests in two ways: the sheath cracks during repeated bending, and the edges chip during low-temperature installation.
2.2 Three Methods of Supplementing, Three Stroke Costs
| Tonifying method | Get what | Cost |
|---|
| ① Toughening (POE / EPDM) | Fracture elongation is recovered along with low-temperature impact | The combustible rubber phase enters the matrix, reducing the flame retardant efficiency; if you still want to pass V-0, you have to add more flame retardant, but increasing the amount pushes down the flexibility that was just restored. |
| ② Replace with a more efficient flame-retardant system (such as certain phosphorus-nitrogen intumescent systems) | Increasing the amount at the same gear can bring it down | Rising costs, narrowing processing window (the decomposition temperature of the flame retardant must match the processing temperature), and some systems show significant moisture absorption |
| ③ Double-layer coextrusion (soft inner layer, flame-retardant outer layer) | Flexibility and flame retardancy are handled separately | With the increase in process complexity, an additional interface needs to be controlled, and wall thickness and eccentricity become more difficult to manage. |
The core judgment is just one sentence: none of these three are free. The question is not 'can they be done simultaneously,' but 'which one to use as a supplement, and whether the cost is acceptable.'
Dare to challenge a common practice: many projects 'first select materials according to V-0, then figure out how to add flexibility.' The order is reversed. What should be determined first is the baseline for flexibility—the minimum installation temperature, the minimum bending radius, and the number of bends. The flame retardancy rating is provided by safety regulations and is fixed; the flexibility baseline is determined by design and installation methods and is flexible.
2.3 Four routes, each managed by one section
| Route | Cost / Boundary | Adapter segment |
|---|
| Halogen-free flame-retardant modified PP sheath | Low density, low cost, recyclable; flexibility upper limit is restricted, long-term use above 90℃ is limited by window constraints | Low-voltage cables and control cables fixed and laid indoors |
| Cross-linked polyolefin (XLPO) | Temperature-resistant, weather-resistant, and stable electrical performance; however, thermosetting cannot be recycled and is difficult to repair. | Halogen-free low-smoke main trunk sections with higher temperature resistance requirements |
| Thermoplastic Elastomer (TPE / TPU) | Soft and smooth, good low-temperature performance, good wear resistance; cost is relatively high, oil resistance and temperature resistance depend on the system. | Flexible cables for frequent movement, drag chains, and reels |
| PVC | Low cost, high softness and processing maturity; contains halogens, releasing hydrogen halides and dense smoke when burned | Conventional low-voltage cables with no halogen requirement |
Text version conclusion: The four types are not substitutes for each other; they have a division of labor. If you require halogen-free, low-smoke, budget-controlled, and fixed installation methods, that is the domain of halogen-free flame-retardant modified PP; if you require extremely flexibility, frequent movement, long-term use above 90°C, or very strict smoke density requirements, then you should go for XLPO, TPE/TPU. The halogen content and smoke generation of PVC when burning should be clarified (public information standard: halogen-containing systems release halogen acid gases at a level of 15-40 mg/g, halogen-free is judged as ≤5 mg/g), but it still holds its place in cost and flexibility — this is a matter of division of labor, not a question of which is better or worse.
3. ★ Selection Criteria Table for Low-Voltage Cable Sheaths: Ten indicators, each with verification method and standard number
The part where choosing a model most often gets stuck is not 'which indicator to look at,' but 'what to use to measure it and how much counts as passing.'
| Indicator | Threshold Value (Typical) | Verification Method · Standard Number | Common Failures | Common solution |
|---|
| Single vertical burning | A single vertical spread-through; bundled laying should follow the requirements for bundling | GB/T 18380.12 (equivalent to IEC 60332-1-2) | Sheath promotes combustion, flame spreads along the cable | Increase the dose, or switch to a more efficient system |
| Halogen-free Low smoke | Halogen acid gas (calculated as HCl) ≤5 mg/g; pH ≥4.3; conductivity ≤10 μS/mm; transmittance ≥60%; bromine <900 ppm, chlorine <900 ppm, total <1500 ppm | GB/T 17650.1, GB/T 17650.2; Smoke density GB/T 17651.2 | Corrosive gases, smoke density exceeding the standard | Halogen-free system, low-smoke filler, no halogen-containing additives added |
| Hot wire (when the whole machine requires it) | GWIT 750 / 775℃; GWFI 850 / 960℃; 850℃ glowing wire contact for 30 s does not ignite | GB/T 5169.13 (GWIT), GB/T 5169.12 (GWFI) | Ignition by hot wire, ignition by droplet | Improve carbonization and flame retardant efficiency |
| Elongation at break (original) | Halogen-free flame-retardant polyolefin sheath material is commonly 150-250% (Class B); sheath threshold is commonly ≥150% | GB/T 2951.11 | White marks and cracks at the bends | Toughening, or reducing the amount of flame retardant added |
| Elongation at break retention after aging | Change rate after 100℃ × 168 h ≤ ±30% | GB/T 2951.12 | New material can bend, but after aging it cannot bend and becomes brittle | Antioxidant system Low-moisture-absorption flame-retardant system |
| Low-temperature winding / Low-temperature stretching | −15 / −25 / −40℃ determined per piece; low-temperature tensile elongation ≥30% | GB/T 2951.14 | Low-temperature installation chipping and cracking | Impact-resistant copolymerization to increase toughness, or switch to a high-flexibility system |
| Heat shrink | Shrinkage rate ≤3% (can be relaxed according to the standard at 80°C setting) | GB/T 2951.13 | Long section directly applied retracting, joint exposing core | Adjust crystallization and cooling, review shrinkage rate |
| High Temperature Pressure (Thermal Deformation) | 80-90℃ indentation depth ≤50% | GB/T 2951.31 | Deformation under high temperature and pressure, sheath puncture | Increase temperature resistance grade Control filler ratio |
| Resistant to mineral oil / Resistant to chemicals | IRM902, 100℃ × 24 h or 168 h; common change rate ≤±40% | GB/T 2951.21 | Swelling and softening in oily environments | Selection of oil-resistant base and system |
| Volume Resistivity / Insulation Resistance | Confirm according to product standards and customer thresholds; for finished products, additionally test the insulation resistance between the conductor and the sheath | GB/T 31838.2 (Equivalent to IEC 62631-3-1) | Insulation decreases and withstand voltage fails after moisture absorption | High-purity, low-ion system Moisture-proof and dry |
Text version of the conclusion: Out of the ten items, there are two that should be looked at first—the retention rate of elongation after aging, and low-temperature winding / low-temperature stretching. The former determines whether the sheath can survive the design lifespan, while the latter determines whether it can be installed on the machine. Selection based only on the original elongation at break is incomplete: sheath failures almost all occur after several years of service.
There is another related point to consider: halogen-free flame-retardant systems (especially expandable types) are prone to moisture absorption, and moisture absorption directly lowers electrical performance (Industry data for Class B: the volume resistivity of halogen-free flame-retardant cable material can decrease by 60-80% after being soaked in water for one day). For this type of sheath, drying, packaging, and storage are all significant matters.
4. Common Failures and Root Causes: Sheath cracking, aging and embrittlement, low-temperature chipping, shrinkage exposing the core
Four phenomena, four root causes; don’t mix up the order of attribution—if you get it wrong, money will be spent in the wrong place.
Failure 1 · Whitening and cracking at bends (appears even with new material). The root cause is mostly not 'brittle material,' but insufficient elongation at break. When the original elongation is around 150%, and the bending radius during installation is designed according to flexible cable requirements, cracking is inevitable. First, look at the bending radius and installation method, then at the material.
Failure Type 2 · New material can bend, but after aging it cannot bend. The root cause is thermal-oxidative aging combined with moisture absorption and hydrolysis of the flame retardant system, causing elongation retention to drop by ±30%. The verification item is the elongation at break after aging according to GB/T 2951.12, not the original value — many projects only test the original value and release it, only to have issues appear two years after installation.
Failure Three · Chipping during low-temperature installation. The root cause is that winding or stretching at low temperatures is not sufficient. PP is already close to brittle in low-temperature zones, and with 25-30% rigid particles added, it becomes a double weakness. This issue should be tested during the small sample stage using winding or stretching at −15 / −25 / −40°C.
Failure Four · The sheath retracts exposing the core, and the printing is worn off. The root cause lies in heat shrinkage and surface wear resistance. After changing the material, the crystallization behavior changed, and the shrinkage changed accordingly; scratch resistance is often tested using the scratch needle method (B-level industry data standards), which is related to both surface hardness and printing process.
Dare to deny the second common practice: some people rely on 'adding two or three more parts of flame retardant' to reliably pass V-0. This is wrong. Increasing the amount further continues to reduce flexibility, increases moisture absorption, and lowers insulation resistance—using the margin for V-0 to compromise flexibility, electrical performance, and lifespan is clearly an uneconomical trade.
5. Verification sequence: For low-voltage cable sheath replacement, first determine safety standards, then determine flame retardancy, and then screen for flexibility
This part is something almost no peers write about, but it determines which step the money is spent on and whether it will eventually explode all at once.
`
① Complete machine safety requirements Flame retardant grade / Halogen-free / Smoke density / Temperature rating / Certification standards
↓ If this level is not clearly set, everything afterwards will be wasted
② Set flame-retardant level and system Single vertical burning (GB/T 18380.12) passed first
↓ Can't get through, return ① Check whether the gear position is set too high
③ Screening Flexibility Elongation at Break (GB/T 2951.11) Low-Temperature Winding/Stretching (GB/T 2951.14)
↓ However, return to ② to change the system or adjust the dosage
④ Retention rate of flexibility after aging Change rate of elongation after 100℃×168 h ≤±30% (GB/T 2951.12)
↓ Not enough, return to ②③ for redistribution of the system
⑤ Electrical Retesting Volume resistivity (GB/T 31838.2) Finished product insulation resistance; retesting in a humid state is recommended
↓ Much more dampness loss, return ② switch to a low moisture absorption system
⑥ Complete Machine Wiring Verification: Bending Radius, Laying Traction, Printing and Color Marking, Terminal Crimping
`
The most common mistake is skipping ③ and ④ and going straight to ⑥. Judging the material flexibility based on finished cables is too costly; skipping the post-aging retention rate is equivalent to leaving the biggest risk to be settled two years later.
Text version of the conclusion: The sequence is safety standards → flame retardancy → flexibility → aging retention → electrical → wiring. The flexibility and aging retention stages must be passed during the small sample phase—they are the most likely to result in outright rejection, and this is also the time when changing the system has the lowest cost.
6. Reverse honesty: For these four types of low-voltage cable sheaths, halogen-free flame-retardant modified PP should not be the first choice
Let's first talk about situations where it shouldn't be used. For the following four types of parts, changing the route is more cost-effective than forcing it.
| The situation that occurred | Why halogen-free flame-retardant modified PP is not suitable | Which way should I go? |
|---|
| Long-term operating temperature requirement: above 90℃ | The temperature resistance window of the PP substrate is around this line, and raising it with filling has a limit. | Cross-linked polyolefin (XLPO) or higher temperature-resistant system |
| Requires extremely high flexibility (frequently moving flexible cables, drag chains, retractable reels) | The opposition between flexibility and flame retardancy cannot be eliminated, and the PP base hardly provides both high flexibility and high flame retardancy at the same time. | TPE / TPU, or high-flex XLPO |
| Requires extremely low smoke density and non-toxicity (crowded areas and tunnel scenarios) | It is difficult for the PP-based system to simultaneously meet the requirements at this very low smoke density level. | Halogen-free low-smoke polyolefin (XLPO) system |
| Requires long-term immersion in oil, strong solvents, or strongly polar media | The medium's erosion of the matrix is systemic, and the formula can't contain it. | Select corrosion-resistant elastomer systems according to the medium |
The pattern is consistent: whenever there are 'two opposing requirements that both need to be met, and enough margin needs to be given for both,' it's time to change course rather than force it with PP. When facing such demands, our approach is to first make this clear, and then discuss whether there is room for compromise—forcing through the order in the end will always result in rework and claims to get it back.
7. What to operate when changing materials: Checklist for first inspecting then operating on the jacket extrusion line
Before the customer decides to try halogen-free flame-retardant modified PP jackets, it is recommended to go through this table first.
| Items to move | What needs to be confirmed | What will happen if I don't do it? |
|---|
| Extrusion Temperature Distribution | The melt viscosity of the flame-retardant system is relatively high, so the barrel and die temperatures need to be increased, but they are limited by the decomposition temperature of the flame retardant. | Surface roughness, pores, release of flame retardants |
| Screw and Shear | Flame-retardant particles are prone to break and disperse unevenly under high shear | Surface pitting, batch-to-batch variation in indicators |
| Drying and packaging | Halogen-free flame retardant systems are obviously hygroscopic, and drying conditions and packaging methods need to be confirmed. | Bubbles, silver streaks, insulation resistance drop |
| Die mold and draw ratio | If the melt strength is different, the draw ratio needs to be reset. | Sheath eccentricity, uneven wall thickness |
| Cooling and Traction | Both the crystallization behavior and the shrinkage rate have changed | Jacket retraction, conductor exposure, dimensional out-of-tolerance |
| Color difference and printing | Interaction between color masterbatch and flame-retardant system; printing adhesion needs re-testing | Batch color difference, print not wear-resistant |
| Verification order | Safety standards → Flame retardant → Flexibility → Aging retention → Electrical → Wiring | All the risks are concentrated to explode at the final step |
Text-based conclusion: Changing materials involves adjusting five process areas: temperature, screw, drying, die, and cooling, plus two aspects for acceptance: color difference and printing. Among them, the validation sequence should be discussed first—first, pass the flexibility and aging tests on small samples before adjusting extrusion parameters.
8. One-page report sheet: Directly paste the conclusion of low-voltage cable sheath material selection into the PPT
The purpose of this form is to allow technicians to report conclusions directly without having to reorganize their language.
| Scene | Recommended Route | Key indicators | Verification Standard | Conditions that need to be confirmed first |
|---|
| Indoors fixed laying of low-voltage control cables | Halogen-free flame-retardant modified PP toughening system | Single fiber vertical burning, elongation at break, retention after aging | GB/T 18380.12, GB/T 2951.11, GB/T 2951.12 | Flame retardant rating, temperature resistance level, minimum bending radius |
| Cabling outdoors or in the equipment room | Halogen-free flame-retardant modified PP weather-resistant system | UV aging resistant, low-temperature winding, halogen-free low smoke | GB/T 16422.2, GB/T 2951.14, GB/T 17650.1/.2 | Minimum ambient temperature, UV exposure level |
| Northern low-temperature installation environment | Increase toughening and dosage, or switch to a higher flexibility system | −25 / −40℃ low-temperature winding or stretching ≥30% | GB/T 2951.14 | Minimum temperature during installation, construction method |
| Long section direct application, tight joint allowance | Adjust crystallization and cooling, review shrinkage rate | Shrinkage rate ≤3% | GB/T 2951.13 | Laying method, joint reserve length |
| High flexibility, frequent movement | Should go with TPE/TPU or high-flex XLPO (not on this route) | No cracking after bending fatigue | Bending fatigue according to IEC 60811-504/JB/T 10491 Approach | Number of bending cycles, minimum bending radius |
Text version Conclusion: There is only one criterion for judgment—can the customer use this chart and determine the material direction in a single meeting?
9. The most common problem with low-voltage cable sheaths is often not flame retardant or not passing
The two most common complaints about sheaths are bend cracking and brittleness after aging, and among these two types, the proportion caused by insufficient flame retardant rating is not high.
The flame retardant threshold is the obvious threshold, with clear criteria: single vertical combustion is GB/T 18380.12, halogen-free is GB/T 17650.1 / GB/T 17650.2. Flexibility is the door on the dark side; many projects have never quantified material selection at all—no minimum installation temperature, no minimum bending radius, no retention rate target after aging.
The industry's common approach is to set four things together: substrate level, toughening system dosage, flame retardant system selection (determines how much can be compressed), and retention rate target after aging. The balance relationship among these four is the real technical challenge for these parts.
Ningbo Kelong New Materials Co., Ltd. commonly supplies halogen-free flame-retardant + toughening directions in modified polypropylene (PP) pellets for this part. According to the flame-retardant level, minimum installation temperature, and bending radius, the base material and flame-retardant system are assigned to the main issue, mainly to solve the aforementioned issues of "over-flame-retardant and flexible collapse"; The formula can be adjusted according to the working conditions of the part, and can be used for sample comparison and post-aging flexibility retention verification. It can also accommodate small-batch multi-variety and small-batch demands from customer-level customers.
FAQ
Q: Can halogen-free flame-retardant PP sheaths be made with V-0 and flexible properties together?
A: Yes, but there is a cost. Toughening lowers flame retardant efficiency, changing systems increases costs and narrows processing windows, and double-layer co-extrusion raises process complexity. The question isn't "can it be done," but "which one to use to compensate for, and whether the cost is acceptable."
Q: What is the elongation at break for your halogen-free flame-retardant PP sheath material?
A: Per piece, not individually. You need to set three thresholds for me: original elongation at break, retention after aging, and low-temperature winding temperature. We set the system based on these three and provide both the original value and the retention value after aging—the data only given to the original value is incomplete when used on the sheath.
Q: Why does our current material bend when new, but becomes brittle after a year of installation?
A: This is the most typical failure of the sheath—retention of flexibility after aging. Two things to check: GB/T 2951.12 (100°C×168 h) whether the rate of change in elongation at break after aging exceeds the ±30% range; Whether the flame-retardant system absorbs too much moisture. Both issues are in the materials and packaging, not in the machine.
wants to remind you: the most common mistake when a part has a problem is to change the material first. Bending and cracking, aging and becoming brittle, low-temperature cracking, shrinkage and core exposure—each has more than one cause. Position first, then change the material; If the order is reversed, often the same thing remains in place after several rounds.
Final words
Low voltage cable sheaths use halogen-free flame-retardant modified PP; flame retardant and flexible are a pair of enemies, no one can avoid them. This doesn't depend on formulation level, but on the 25-30% flame-retardant dosage.
The question is not "can both be achieved," but "which one to use to compensate for, and whether the cost is acceptable." Toughening, system change, double-layer co-extrusion—all three paths need to be accounted for.
The order of validation is more important than the validation items. Safety regulations→ flame retardant → Flexible → Aging retention → Electrical → wiring; Flexibility and aging retention must be passed during the sample stage.
About Us
Same grade, but two companies produce different products—what's the problem?
is the same material, but the process is two different sets. Drying, extrusion temperature, screw assembly, die and cooling—if any one is off, the result is two different lines. Choosing the right material only means you're half the battle.
Ningbo Kelong New Materials Co., Ltd. produces modified polypropylene (PP) granulation, covering three grades: homopolymer, random copolymer, and impact-resistant copolymer. It also covers three grades: filling, glass fiber reinforcement, toughening, flame retardancy, low odor and low VOC, weather resistance, and no coating or scratch resistance. Also operates PP resin, sub-brand materials, and large package materials for major petrochemical plants.
