光伏接线盒、连接器用什么改性PP？答案不是单过 V0，而是耐候与阻燃两道门槛同时过——而它们互相拉扯。这篇讲清无卤阻燃、玻纤增强无卤阻燃、工程塑料三线的分工，以及为什么双门槛的冲突必须用验证顺序来解、哪三种工况不该用改性PP。
一个做光伏接线盒的工程师问我：我们户外接线盒，现在用的料要么耐候够但过不了 V0，要么阻燃够了、在院子里放两年一掰就碎，这俩到底怎么同时保住？
这话里的问题，正是光伏接线盒选改性 PP 最容易卡住的地方：它要过的不是一道门槛，是两道——户外耐候和电气阻燃，而且这两道门是互相拉扯的，不是简单地"两个都加足"就能解决。
下面按工况、路线、判据、验证、边界五层往下拆。
一、光伏接线盒厂最常问的一句话：既要 V0 又要耐 25 年户外，怎么调？
把接线盒／连接器的工况拆成六维，六个数报齐，材料方向基本就定了。这个件的特殊点在于：它一边在屋顶暴晒，一边贴着二极管的发热源，两股工况摞在同一个壳体上。
| 维度 | 接线盒／连接器实际工况 | 对改性 PP 的要求 |
|---|
| 温度 | 内部二极管发热，盒体长期 80–105℃；屋顶环境夏季可更高；存在局部热点 | RTI≥105℃；耐热老化 |
| 载荷 | 线缆夹紧力、插拔力、振动与风载传递 | 一定刚性、尺寸稳定、抗蠕变 |
| 介质 | 雨水、凝露、盐雾、灰尘积附；内部可能有密封脂 | 耐湿热、耐盐雾、绝缘保持 |
| 寿命 | 随组件按 25 年设计寿命 | 长期老化后性能不塌 |
| 外观 | 壳体变色、粉化被客户与运维看见 | 氙灯老化 ΔE≤3.0 |
| 合规 | 阻燃 V0 + 灼热丝；电气安全与防火 | 无卤阻燃 + 灼热丝 + RTI 齐过 |
六维里，温度和合规是"一票否决"性质的——前者卡长期耐热，后者卡着火与电气安全。耐候（介质＋寿命＋外观）不是锦上添花，是 25 年户外服役的底线。把这两类门槛当成"加两种助剂"来理解，就走偏了。
文字版结论：接线盒的工况硬线有三条——内部 80–105℃ 对应的 RTI≥105℃、屋顶紫外＋湿热对应的耐候保持率、以及电气侧 UL94 V-0 与灼热丝。三条缺任何一条，件都进不了组件。光伏组件按 IEC 61215（设计鉴定与定型）／ IEC 61730（安全鉴定）体系认证（A 级标准），接线盒与连接器另有 IEC 62790／IEC 62852 组件标准（据行业技术资料，B 级）；25 年设计寿命由此而来。
二、材料路线对比：无卤阻燃 PP、玻纤增强无卤阻燃、工程塑料三线分工不冲突
接线盒／连接器能落在三条路线上，没有"谁更好"，只有"卡在哪条线"。
| 路线 | 拿到什么 | 代价／短板 | 适用 |
|---|
| 无卤阻燃 PP 体系（不加玻纤） | 过 V0、轻、成本低；成型好 | 刚性偏低，长期 80–105℃ 下尺寸与蠕变要核；耐候体系要和阻燃体系配平 | 中小电流接线盒壳体、对内强度要求不极端 |
| 玻纤增强 ＋ 无卤阻燃 | 刚性、尺寸稳定、抗蠕变提升；更扛内部发热 | 浮纤、各向异性、翘曲；对模具与工艺敏感 | 大电流、厚壁、受力件；连接器本体 |
| 工程塑料（PA66／PBT 等） | 耐热、刚性、耐候与电气综合更强，CTI 高 | 成本高、密度高；与 PP 路线不在一个价档 | 高电流、超高 CTI、长期高温且常户外的高端场景 |
先说无卤的量化定义，这是绕不开的硬指标：溴 <900 ppm、氯 <900 ppm、两者总和 <1500 ppm。满足这条才叫无卤。
灼热丝指标也要记准：GWIT 750／775℃；GWFI 850／960℃。其中 850℃ 灼热丝接触 30 s 不引燃 这一条，比单纯过 V0 更贴近接线盒内部电气密集的工况——盒内二极管发热、电弧风险真实存在，单拿 V0 报告去谈"安全"，在光伏件上是不够的。
文字版结论：PP 路线靠"无卤阻燃 ＋（可选）玻纤增强"能覆盖大多数接线盒；当工况进入高电流、超高 CTI 且长期户外的区间，工程塑料的综合性才显出来。三线是分工，不是替代——选哪条，看件最怕哪一项。
三、★ 选型判据表：接线盒料要过的五项判据，每项都带验证方法
接线盒料要同时过耐候与阻燃五项判据，每一项都必须带验证方法——选料卡住常不是不知道看哪项，是不知道拿什么测、测到多少算过。（标准号按通行引用，具体以牌号 TDS／实测报告为准）
| 指标 | 门限值 | 验证方法 · 标准号 | 常见失效 | 通行解法 |
|---|
| UL94 V-0 | V-0（规定厚度，离火自熄、不引燃脱脂棉） | GB/T 2408／IEC 60695-11-10（UL94） | 燃烧熔滴引燃周边 | 无卤膨胀阻燃体系 |
| 850℃ 灼热丝 30s 不引燃 | GWFI 850/960℃；接触 30s 不起燃 | IEC 60695-2-12/13；GB/T 5169 系列（GWIT/GWFI） | 灼热丝接触即引燃 | 玻纤增强 ＋ 无卤阻燃 |
| RTI 长期使用温度 | RTI ≥105℃（对应内部 80–105℃） | UL 746B 相对耐热指数（长期热老化外推） | 长期服役变脆 | 耐热体系 ＋ 玻纤增强 |
| 户外耐候保持 | UV＋热老化 500–1000 h 后性能不下降；氙灯 ΔE≤3.0 | GB/T 16422.2（氙灯老化）；IEC 61215/61730 体系 | 变色、粉化、脆化 | UV 吸收剂 ＋ 受阻胺光稳定剂（HALS） |
| 电气绝缘（CTI／体积电阻率） | CTI 达额定等级；体积电阻率保持 | GB/T 4207／IEC 60112（CTI） | 漏电起痕、击穿 | 无卤阻燃 ＋ 绝缘厚度设计 |
文字版结论：五项里 850℃ 灼热丝、RTI 和户外耐候保持是优先看的三道——普通磷氮阻燃 PP 只够 V0，后两道常过不了，而耐候保持又会被阻燃体系反噬（详见第五节）。门限值和验证方法一起看，缺一项不判合格，比样件试出来再回头找原因省钱得多。
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顺带说明边界：开关插座面板的 CTI 高等级与耐漏电起痕专项在 PP-A17 讲，本篇只在点连接器的"户外 ＋ 接线盒内部高温电气"场景，不展开 CTI 高等级路线。
四、常见失效与根因：把阻燃剂和耐候剂一起加满，是接线盒典型的错法
四类失效里，典型的一种错法是"把阻燃剂和耐候剂一起加满"——这是双门槛最常见的翻车来源。
失效一：V0 过了、灼热丝挂了。 根因是普通磷氮阻燃 PP 只够 V0，炭层和耐热撑不到 850℃ 热点；没上玻纤增强，热变形也兜不住。解法不是再加阻燃剂，是补刚性和耐热骨架。
失效二：户外放两年一掰就碎。 根因常在耐候——紫外与热氧让分子链降解，冲击掉下来。但这里有个坑：很多人以为是光稳定剂加少了，往里猛加 HALS 和 UV 吸收剂，结果还是裂。因为真正拖后腿的是阻燃剂本身在加速老化，见下节。
失效三（敢否定一个常见做法）：把阻燃剂和耐候剂"两个都加满"来同时过双门槛。 这是错的。含卤阻燃剂、以及部分磷系阻燃剂，自身会促进热氧老化，还会和光稳定剂抢位——你加得越多，光稳定剂能发挥的空间越小。双门槛的冲突不是"量不够"，是"两类助剂在同一体系里互相拆台"。靠堆量硬上，常常阻燃过了、耐候反而更差。
失效四：湿热后绝缘下降、起痕。 盒体长期凝露、积灰、盐雾，阻燃与填料体系若没核算介质耐受，绝缘电阻会掉。根因是只盯了阻燃忘了电气长期行为。
五、验证顺序：先锁阻燃三关再验耐候，顺序反了双门槛解不开
双门槛能不能同时过，关键在验证顺序——顺序错了，成本在最后一步集中爆。
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① 小样物理比对 拉伸 / 弯曲 / 缺口冲击 / 收缩率 / 阻燃 V0
↓ 五项在门限内，才往下走
② 灼热丝 + RTI 850℃ 30s 不引燃；RTI≥105℃
↓ 这两关不过，后面全不用做
③ 耐候验证 在"已定阻燃体系"上做 UV+热老化 500–1000h
↓ 看 ΔE、力学保持；不过则调光稳定剂/换阻燃体系，不靠加量
④ 短射试模 看充填、熔接线、浮纤
↓ 短射走通，才谈批量
⑤ 装配合规 + 批量试产
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文字版结论：验证顺序是 小样→灼热丝/RTI→耐候→短射→批量。耐候必须在"阻燃体系已锁定"的前提下验，这样才能把"阻燃剂拖耐候后腿"这件事暴露出来、定向调光稳定剂或换更温和的阻燃体系；顺序反了，你永远分不清是两关谁在拖谁。
六、反向诚实：长期 150℃ 以上、超高 CTI 且常户外、或要金属级导热，接线盒别用改性 PP
前面讲"怎么做"，这里讲"什么时候别做"。这一段对选型判断价值最高。
| 出现的情况 | 为什么改性 PP 不合适 | 该往哪走 |
|---|
| 要求长期工作温度 150℃ 以上 | 改性 PP 的耐热上限就在那条线附近，增强也抬不太多 | 换 PA46／PA6T 等更高耐热的工程塑料 |
| 要求 超高 CTI 且长期户外 | PP 绝缘好但 CTI 受填料／阻燃剂拖累，高等级难稳 | 走 PBT／PA66 等 CTI 天然高的工程塑料 |
| 要求 金属级导热／电磁屏蔽 | PP 是热与电的不良导体，改性只能小幅改善 | 金属壳体或导热／屏蔽专用材料 |
| 要求 A 级外观 ＋ 高阻燃同时 | 高表面要少填料少浮纤，高阻燃要高填充，两方向对拉 | 表面件与阻燃件分开设计，或换料 |
文字版结论：这几种工况的共同点是"两个方向相反的要求同时要"——长期高温＋塑料、超高 CTI＋常户外、塑料＋金属级导热。任一出现就说明这个件不该用 PP 硬撑；先说清楚，再谈折中，硬接下来的单子最后都要用返工还回去。
七、换料风险清单：接线盒换料要动的七项，验证顺序排第一
决定试改性 PP 之前，这张表建议先过一遍。客户真正顾虑往往不是性能，是"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 | 玻纤料与纯阻燃料收缩率差，壳体尺寸敏感 | 尺寸超差，装配对不上 |
| 浇口与排气 | 玻纤料流动差异，熔接线位置变 | 充填不足、熔接线弱 |
| 料温与模温 | 阻燃＋玻纤体系窗口不同；阻燃料停留时间要控 | 浮纤、炭化、熔接线差 |
| 干燥 | 按具体体系定，阻燃料停留时间要控 | 银丝、气泡、降解 |
| 保压与脱模 | 收缩差异带来变形与顶白 | 变形、顶出拉伤 |
| 色差 | 壳体是可见件，必须先确认色板 | 批次色差争议 |
| 验证顺序 | 小样→灼热丝/RTI→耐候→短射→批量 | 风险全压到最后一步爆发 |
文字版结论：换料要动的是模具、工艺、色差三块，关键的是验证顺序。跳过小样直接试模，等于把成本提前花出去；跳过耐候验证直接批量，一次失效就是整批召回级别的代价（光伏件更换要高空作业）。
八、一页纸汇报对照表：四类接线盒场景直接给技术员上报
| 场景 | 推荐路线 | 关键指标 | 验证标准 | 需先确认的条件 |
|---|
| 常规户外接线盒 | 无卤阻燃 PP 体系 | V0 ＋ 850℃ 灼热丝 ＋ 户外耐候 ΔE≤3.0 | GB/T 2408；IEC 60695-2；GB/T 16422.2 | 内部长期温度、是否含玻纤增强 |
| 大电流／厚壁件 | 玻纤增强 ＋ 无卤阻燃 | V0 ＋ RTI≥105℃ ＋ 尺寸稳定 | 同上 ＋ UL 746B | 电流等级、螺栓位受力 |
| 连接器本体 | 玻纤增强无卤阻燃（或工程塑料） | V0 ＋ CTI ＋ 耐插拔 | GB/T 4207；IEC 62852 | 插拔力、CTI 等级 |
| 高等级／极端户外 | 工程塑料（PA66/PBT） | 超高 CTI ＋ 长期高温 | IEC 62790/62852 | 是否超 PP 边界 |
文字版结论：这张表让技术员能把结论直接往上报，不必重组织语言。判断标准只有一条——客户拿这张表，能不能一次会议里把材料方向定下来。
九、接线盒的耐候阻燃双门槛，难在体系配平
行业里接线盒最常见的翻车，不是 V0 过不了，是 V0 过了、在户外放一两年开裂，或者灼热丝挂了。据艾邦高分子等公开技术资料（B 级），光伏接线盒的判据落在 UL94 V-0 ＋ 850℃ 灼热丝 30s 不引燃 ＋ RTI≥105℃ 三关，加上户外 UV＋热老化 500–1000h 后的性能保持；普通磷氮阻燃 PP 常卡在后两道。
这里有个结构性判断必须讲清：PP 阻燃剂加量普遍在 25–30% 这一档。"阻燃剂加得多、力学就一定掉"是 PP 的结构性问题，不是配方水平问题。 更麻烦的是含卤与部分磷系阻燃剂会加速老化、与光稳定剂抢位——所以双门槛的冲突，用验证顺序解、不用"两个都加足"解：先锁阻燃三关，再在已定阻燃体系上验耐候，失败就定向调光稳定剂或换更温和的阻燃体系。
宁波市科隆新材料有限公司在这个件上常供的是无卤阻燃改性 PP 与玻纤增强无卤阻燃方向，主要用来解决"耐候与阻燃同时过 ＋ 尺寸稳定"这两件事；配方按件的工况调，可以陪客户一起做小样比对与耐候／灼热丝验证，多品种小批量的件级需求也能接。
常见问答
问：无卤和有卤怎么选？只看成本行不行？
答：不行。有卤（溴系）效率高、加量少、成本低，但加工受热释放卤化氢腐蚀设备模具，燃烧释放卤化氢与浓烟，而且对接线盒的耐候与灼热丝不利。无卤更稳，代价是力学和成本要让。光伏件走无卤是行业通行方向。
问：阻燃剂加得多力学掉，是你们改性 PP 配方不行吗？
答：不是配方水平问题，是 PP 底子的结构。加量 25–30% 是 PP 绕不开的档，降不下来。能做的只是在这个前提下把阻燃体系选温和、把光稳定剂配平，让耐候损失可控。
问：户外两年开裂，是不是光稳定剂加少了？
答：不一定。先排除阻燃剂在拖后腿——含卤、部分磷系阻燃剂会促进热氧老化、和 HALS 抢位。正确做法是把阻燃体系锁定后单独验耐候，判断失效来自哪一类助剂，再定向调整，而不是无脑加量。
| 工况 | 关键判据 | 科隆常规供应 |
|---|
| 常规户外接线盒 | V0 ＋ 850℃ 灼热丝 ＋ 户外耐候 ΔE≤3.0 | 无卤阻燃 PP，常规备货 |
| 大电流／厚壁件 | V0 ＋ RTI≥105℃ ＋ 尺寸稳定 | 玻纤增强无卤阻燃 PP 方向 |
| 高等级电气件 | 高 CTI ＋ 长期高温 | 按工况评估，或建议工程塑料路线 |
想提醒一句：件出问题，常见的错法是先换料。变色、开裂、灼热丝挂——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。
十、最后说三句
一、光伏接线盒选改性 PP，过的是两道互相拉扯的门槛，不是一道 V0。耐候与阻燃、RTI 与灼热丝，少一道都不算过关。
二、双门槛的冲突用验证顺序解，不用"两个都加足"解。先锁阻燃三关，再在已定体系上验耐候；失败定向调光稳定剂或换更温和的阻燃体系，而不是堆量。
三、超过 PP 边界的工况，别硬撑。长期 150℃ 以上、超高 CTI 且常户外、或要金属级导热屏蔽——这些该走工程塑料或金属，先把这条讲清楚再谈方案。
下一篇讲光伏逆变器壳体——那个件阻燃和 CTI 的账，算法又不一样。
关于我们
这三件事我们从不猜：耐温、寿命、用量。
没给使用温度，不猜；没给服役时长，不猜；没说月用量，也不猜。猜出来的方案，最后都要用返工和索赔还回去。
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 type of modified PP is used for photovoltaic junction boxes and connectors? The answer is not just passing the V0 rating, but meeting both weather resistance and flame retardancy requirements simultaneously—which can conflict with each other. This article explains the division of labor among halogen-free flame retardant, glass fiber reinforced halogen-free flame retardant, and engineering plastics, as well as why the conflict between the two requirements must be resolved through a verification sequence, and which three conditions should not use modified PP.
An engineer who makes photovoltaic junction boxes asked me: For our outdoor junction boxes, the materials we currently use either have enough weather resistance but can't pass V0, or they're flame retardant enough but if you leave them in the yard for two years, they break apart whenever touched. How can we possibly keep both properties at the same time?
The problem in this statement is exactly the point where choosing modified PP for photovoltaic junction boxes is most likely to get stuck: it has to pass not one threshold, but two—outdoor weather resistance and electrical flame retardancy, and these two thresholds pull against each other, it’s not simply a matter of 'just fully meeting both' that can solve it.
Next, we break it down into five levels: operating conditions, routes, criteria, verification, and boundaries.
1. The most frequently asked question at PV junction box factories: How do you make it both V0 and withstand 25 years outdoors?
Break down the operating conditions of the junction box/connector into six dimensions. When all six numbers are reported, the material orientation is basically determined. The special point of this part is that one side is exposed to the sun on the roof, while the other side is next to the heat source of the diode. Two sets of operating conditions are stacked in the same housing.
| Dimension | Junction box/connector actual working conditions | Requirements for modified PP |
|---|
| Temperature | The internal diode generates heat, the case temperature is 80–105°C for long periods; the rooftop environment can be higher in summer; local hotspots exist | RTI ≥ 105°C; heat aging resistance |
| Load | Cable clamping force, plug-in and pull-out force, vibration and wind load transmission | Certain rigidity, dimensional stability, creep resistance |
| Medium | Rainwater, condensation, salt spray, dust accumulation; there may be sealing grease inside | Moisture and heat resistance, salt spray resistance, insulation retention |
| Lifespan | Designed service life of 25 years with components | Performance does not deteriorate after long-term aging |
| Appearance | The casing discoloration and chalking were noticed by customers and operations and maintenance staff | Xenon lamp aging ΔE≤3.0 |
| Compliance | Flame retardant V0 Glow wire; electrical safety and fire prevention | Halogen-free flame retardant, glowing wire, RTI all passed |
In the six dimensions, temperature and compliance are of a 'veto' nature — the former limits long-term heat resistance, and the latter controls fire and electrical safety. Weather resistance (medium + lifespan + appearance) is not a luxury; it is the baseline for 25 years of outdoor service. Treating these two types of thresholds as 'just adding two additives' is a misunderstanding.
Text version conclusion: There are three hardline conditions for the junction box—internal 80–105°C corresponding to RTI≥105°C, roof UV plus damp heat corresponding to weathering retention, and electrical side UL94 V-0 and hot wire. If any of the three are missing, the part cannot enter the module. Photovoltaic modules are certified according to the IEC 61215 (design qualification and type approval) / IEC 61730 (safety qualification) system (Class A standard), while junction boxes and connectors have separate IEC 62790 / IEC 62852 module standards (according to industry technical information, Class B); the 25-year design life comes from this.
2. Comparison of material routes: halogen-free flame-retardant PP, glass fiber reinforced halogen-free flame-retardant, and engineering plastics three-line division of labor does not conflict
The junction box/connector can fall on any of the three routes; there is no 'which is better,' only 'which line it gets stuck on.'
| Route | Get what | Cost / Shortcoming | Applicable |
|---|
| Halogen-free flame-retardant PP system (without glass fiber) | Pass V0, light, low cost; good molding | Low rigidity; the dimensions and creep need to be checked under long-term 80–105°C; the weather-resistant system should be balanced with the flame-retardant system. | The casing of small and medium current junction boxes does not require extreme internal strength. |
| Glass fiber reinforced + halogen-free flame retardant | Increased rigidity, dimensional stability, and creep resistance; better withstands internal heat generation | Floating fibers, anisotropy, warping; sensitive to molds and processes | High current, thick wall, load-bearing part; connector body |
| Engineering plastics (PA66/PBT, etc.) | Better overall heat resistance, rigidity, weather resistance, and electrical properties, with high CTI | High cost, high density; not in the same price range as the PP route | High current, ultra-high CTI, long-term high temperature, and high-end scenarios that are often outdoors |
First, let's talk about the quantitative definition of halogen-free, which is an unavoidable hard standard: bromine <900 ppm, chlorine <900 ppm, and the total of both <1500 ppm. Only if this is met can it be called halogen-free.
The glow-wire index must also be accurately recorded: GWIT 750/775°C; GWFI 850/960°C. Among them, the requirement that the 850°C glow wire does not ignite after 30 seconds of contact is closer to the actual conditions inside the junction box than simply meeting V0—inside the box, diode heating and arc risks are real. Simply using the V0 report to claim 'safety' is not sufficient for photovoltaic components.
Text Version Conclusion: The PP route relying on 'halogen-free flame retardant + (optional) glass fiber reinforcement' can cover most junction boxes; only when the working conditions enter the range of high current, ultra-high CTI, and long-term outdoor exposure do the comprehensive properties of engineering plastics become apparent. The three lines are for division of labor, not substitution — which one to choose depends on which aspect the part fears most.
3. ★ Selection Criteria Table: Five criteria that the junction box material must meet, each with a verification method
Junction box materials must simultaneously meet both the weather resistance and flame retardant criteria for five items, and each item must include a verification method — when selecting materials, the problem is often not knowing which item to look at, but not knowing what to test or what value counts as passing. (The standard number is cited according to common practice; specific details should be based on the grade TDS/actual test report)
| Indicator | Threshold value | Verification Method · Standard Number | Common Failures | Common solution |
|---|
| UL94 V-0 | V-0 (specified thickness, self-extinguishing when removed from flame, does not ignite cotton wadding) | GB/T 2408／IEC 60695-11-10 (UL94) | Molten droplets from combustion ignite the surroundings | Halogen-free intumescent flame retardant system |
| 850℃ glowing wire 30s does not ignite | GWFI 850/960℃; contact for 30s does not ignite | IEC 60695-2-12/13; GB/T 5169 series (GWIT/GWFI) | Ignites upon contact with hot wire | Glass fiber reinforced + halogen-free flame retardant |
| RTI long-term use temperature | RTI ≥105°C (corresponding to internal 80–105°C) | UL 746B Relative Heat Resistance Index (Long-term Thermal Aging Extrapolation) | Becomes brittle after long-term use | Heat-resistant system + glass fiber reinforcement |
| Outdoor weather resistance | No performance degradation after UV + thermal aging for 500–1000 hours; Xenon lamp ΔE ≤ 3.0 | GB/T 16422.2 (Xenon Lamp Aging); IEC 61215/61730 System | Discoloration, powdering, brittleness | UV Absorber + Hindered Amine Light Stabilizer (HALS) |
| Electrical Insulation (CTI / Volume Resistivity) | CTI reaches the rated level; volume resistivity is maintained | GB/T 4207 / IEC 60112 (CTI) | Tracking and breakdown due to leakage | Halogen-free flame retardant + insulation thickness design |
Text version conclusion: Among the five items, the three priorities are the 850°C glow wire, RTI, and outdoor weather resistance—ordinary phosphorus-nitrogen flame-retardant PP is only enough for V0, the latter two often fail, and weather resistance can be compromised by the flame-retardant system (see Section 5 for details). Threshold values and verification methods should be considered together; missing any one item is considered non-compliant. This approach saves much more money than testing samples first and then going back to find the reason.
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By the way, to clarify the boundaries: the high CTI rating of switch and socket panels and the special resistance to tracking against leakage are discussed in PP-A17. This article only focuses on the 'outdoor + high-temperature electrical inside junction boxes' scenario for connectors and does not expand on the high CTI rating route.
4. Common Failures and Root Causes: Filling the junction box with both flame retardants and weather-resistant agents is a typical mistake.
Among the four types of failures, a typical mistake is 'adding both the flame retardant and the weathering agent all at once' — this is the most common source of failure for the dual threshold.
Failure 1: V0 passed, heating wire burned out. The root cause is that ordinary phosphorus-nitrogen flame-retardant PP is only sufficient for V0; the carbon layer and heat resistance cannot withstand hotspots of 850°C; without glass fiber reinforcement, thermal deformation also cannot be prevented. The solution is not to add more flame retardant, but to supplement rigidity and a heat-resistant framework.
Failure 2: Outdoors for two years and it breaks as soon as you snap it. The root cause is often weather resistance—UV and thermo-oxidation degrade the molecular chains, leading to breakage under impact. But here’s a pitfall: many people think it’s because not enough light stabilizer was added, so they add a lot of HALS and UV absorbers, yet it still cracks. The real culprit slowing things down is the flame retardant itself accelerating aging, as discussed in the next section.
Mistake Three (daring to question a common practice): 'adding both flame retardants and weathering agents to the maximum' to pass both thresholds simultaneously. This is wrong. Halogen-containing flame retardants and some phosphorus-based flame retardants can promote thermal-oxidative aging and compete for positions with light stabilizers—the more you add, the less space light stabilizers have to function. The conflict between the two thresholds is not 'not enough amount,' but 'the two types of additives interfere with each other in the same system.' Simply piling them on often results in passing the flame retardancy requirement but degrading weather resistance.
Failure 4: Insulation deterioration and tracking after moisture and heat. The enclosure experiences long-term condensation, dust accumulation, and salt spray; if the flame retardant and filler system do not account for the medium's tolerance, the insulation resistance will drop. The root cause is focusing only on flame retardancy and forgetting the long-term electrical behavior.
5. Verification sequence: first lock the flame-retardant three-stage lock, then check the weather resistance. If the order is reversed, the double thresholds cannot be opened.
Whether both thresholds can be passed at the same time depends on the verification order—if the order is wrong, the cost will explode in the final step.
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① Sample physical comparison Tensile / Bending / Notched impact / Shrinkage / Flame retardant V0
↓ Only proceed further if all five items are within the threshold
② Glowing wire RTI 850℃ 30s does not ignite; RTI ≥105℃
↓ If you don't pass these two levels, you don't need to do the rest.
③ Weathering Verification Perform UV thermal aging for 500–1000 hours on the 'established flame-retardant system'
↓ Check ΔE and mechanical retention; if not adequate, adjust the light stabilizer or change the flame retardant system, without increasing the dosage.
④ Short shot mold test Check filling, weld lines, and floating fibers
↓ Short-shooting needs to work first before talking about mass production
⑤ Assembly Compliance Mass Trial Production
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Text version conclusion: The verification sequence is sample → hot wire/RTI → weather resistance → short shot → mass production. Weather resistance must be tested under the premise that the flame-retardant system is already locked, so that the issue of 'the flame retardant dragging down weather resistance' can be exposed, allowing for targeted adjustment of stabilizers or switching to a milder flame-retardant system; if the sequence is reversed, you'll never know which of the two is holding back the other.
6. Reverse Honesty: For long-term use above 150°C, with extremely high CTI and frequently outdoor, or requiring metal-level thermal conductivity, do not use modified PP for junction boxes.
Earlier, we talked about 'how to do it'; here, we talk about 'when not to do it.' This section is the most valuable for making selection decisions.
| The situation that occurred | Why modified PP is not suitable | Which way should I go? |
|---|
| Requires a long-term operating temperature above 150℃ | The heat resistance limit of modified PP is around that line, and reinforcement doesn't raise it much. | Replace with higher heat-resistant engineering plastics such as PA46/PA6T |
| Requires ultra-high CTI and long-term outdoor use | PP has good insulation, but its CTI is dragged down by fillers/flame retardants, making high grades difficult to stabilize. | Use PBT/PA66 and other engineering plastics with naturally high CTI |
| Requirements: metal-grade thermal conductivity/electromagnetic shielding | PP is a poor conductor of heat and electricity, and modification can only slightly improve it. | Metal housing or materials dedicated to heat conduction/shielding |
| Requires Class A appearance + high flame retardancy at the same time | High surface requires less filler and less floating fiber, high flame retardancy requires high filling, biaxial drawing | Design the surface parts and flame-retardant parts separately, or change the material |
Text version conclusion: The common point of these working conditions is 'the two opposing requirements must be met simultaneously' — long-term high temperature + plastic, ultra-high CTI + regular outdoor use, plastic + metal-level thermal conductivity. The appearance of any one of these indicates that this part should not be rigidly made with PP; clarify this first, then discuss compromises, otherwise the subsequent orders that are rigidly made will have to be reworked and returned.
7. Material Change Risk List: The seven items to be changed in the junction box, with the verification sequence listed first
Before deciding to try modifying PP, it is recommended to go through this table first. Customers' real concern is often not performance, but whether 'the mold and process need to be changed'.
| Items to move | What needs to be confirmed | What will happen if I don't do it? |
|---|
| Mold shrinkage rate | The shrinkage rates of fiberglass material and pure flame-retardant material differ, making the housing dimensions sensitive. | The dimensions are out of tolerance, and the assembly does not fit. |
| Gate and Venting | Differences in fiberglass flow cause changes in weld line positions | Insufficient filling, weak weld lines |
| Material Temperature and Mold Temperature | Flame retardant + fiberglass system varies by window; the residence time of flame retardant must be controlled | Floating fibers, carbonization, welding line defects |
| Dry | According to the specific system, the residence time of the flame retardant must be controlled. | Silver threads, bubbles, degradation |
| Pressure Holding and Demolding | Shrinkage differences cause deformation and surface whitening | Deformation, extrusion strain |
| Color difference | The casing is a visible part and the color swatch must be confirmed first. | Batch color difference dispute |
| Verification order | Sample → Heating wire / RTI → Weather resistance → Short shot → Mass production | All the risk is pushed to the final step before it explodes |
Text Version Conclusion: Changing materials involves three areas: molds, processes, and color difference, with the key being the verification sequence. Skipping small samples and going directly to mold testing is equivalent to spending the cost upfront; skipping weather resistance verification and going directly to mass production means that a single failure could result in the cost of recalling the entire batch (replacing photovoltaic components requires work at height).
8. One-page report comparison table: Directly report the four types of junction box scenarios to the technician
| Scene | Recommended Route | Key indicators | Verification Standard | Conditions that need to be confirmed first |
|---|
| Standard outdoor junction box | Halogen-free flame-retardant PP system | V0 + 850℃ glowing wire + outdoor weather resistance ΔE≤3.0 | GB/T 2408; IEC 60695-2; GB/T 16422.2 | Internal long-term temperature, whether it contains glass fiber reinforcement |
| High current / thick-walled parts | Glass fiber reinforced + halogen-free flame retardant | V0 + RTI ≥ 105℃ + Dimensional Stability | Same as above + UL 746B | Current rating, bolt position force |
| Connector body | Glass fiber reinforced halogen-free flame retardant (or engineering plastic) | V0 + CTI + Plug and Play Durability | GB/T 4207; IEC 62852 | Insertion and extraction force, CTI rating |
| High-level / Extreme Outdoor | Engineering Plastics (PA66/PBT) | Ultra-high CTI + long-term high temperature | IEC 62790/62852 | Whether it exceeds the PP boundary |
Text version conclusion: This table allows technicians to report conclusions directly without having to reorganize their language. There is only one criterion for judgment—whether the client can determine the direction of the materials in a single meeting using this table.
9. The weather-resistant and flame-retardant double threshold of the junction box is difficult in terms of system balance.
The most common failures of junction boxes in the industry are not that they fail V0, but that they pass V0 and then crack after being outdoors for a year or two, or the glow wire burns out. According to publicly available technical data from companies like AiBang Polymer (Class B), the criteria for photovoltaic junction boxes are UL94 V-0 + 850℃ glow wire 30s non-ignition + RTI≥105℃ three tests, along with performance retention after outdoor UV + thermal aging for 500–1000 hours; ordinary phosphorus-nitrogen flame-retardant PP often gets stuck on the latter two points.
There is a structural judgment that must be clarified here: the addition of flame retardants in PP is generally in the range of 25–30%. The idea that 'adding more flame retardant will definitely reduce mechanical properties' is a structural issue of PP, not a formulation-level issue. What's more troublesome is that halogen-containing and some phosphorus-based flame retardants can accelerate aging and compete with light stabilizers—so the double-threshold conflict should be resolved through the verification sequence, not by 'maxing out both': first lock down the three aspects of flame retardancy, then validate weather resistance on the established flame retardant system; if it fails, then selectively adjust the light stabilizer or switch to a milder flame retardant system.
Ningbo Cologne New Materials Co., Ltd. commonly supplies halogen-free flame-retardant modified PP and glass fiber reinforced halogen-free flame-retardant materials for this type of part, mainly used to address both "weather resistance and flame retardancy plus dimensional stability"; the formulation is adjusted according to the working conditions of the part, and they can work with customers to make small samples for comparison and weathering/burn-wire testing. They can also handle small-batch, multi-variety part-level demands.
Frequently Asked Questions
Q: How to choose between halogen-free and halogen-containing? Is it okay to just look at the cost?
Answer: No. Halogenated (bromine-based) types are efficient, require less addition, and are low-cost, but during processing, heat releases hydrogen halides that corrode equipment and molds; when burning, they release hydrogen halides and dense smoke, and they are also unfavorable for the weather resistance of junction boxes and heating wires. Halogen-free types are more stable, but the trade-off is that mechanical properties and cost suffer. The photovoltaic industry generally follows the halogen-free approach.
Question: If too much flame retardant is added and the mechanical properties drop, is it because your modified PP formula is not good?
Answer: It's not a formula-level issue; it's the structure of the PP substrate. Increasing the amount by 25–30% is a barrier that PP cannot bypass and cannot be reduced. What can be done is, under this premise, to choose a mild flame retardant system and balance the light stabilizers so that the weathering loss is controllable.
Question: Outdoor cracking after two years, is it because too little light stabilizer was added?
Answer: Not necessarily. First, rule out the flame retardant as the limiting factor — halogen-containing and some phosphorus-based flame retardants can accelerate thermo-oxidative aging and compete with HALS. The correct approach is to lock in the flame-retardant system and then test weather resistance separately, determine which type of additive is causing the failure, and then make targeted adjustments, rather than mindlessly increasing the amount.
| Operating condition | Key criterion | Cologne regular supply |
|---|
| Standard outdoor junction box | V0 + 850℃ glowing wire + outdoor weather resistance ΔE≤3.0 | Halogen-free flame-retardant PP, regular stock |
| High current / thick-walled parts | V0 + RTI ≥ 105℃ + Dimensional Stability | Glass fiber reinforced halogen-free flame-retardant PP direction |
| High-grade electrical components | High CTI + Long-term high temperature | Evaluate according to working conditions, or suggest an engineering plastic route |
Just a reminder: when something goes wrong, a common mistake is to change the material first. Discoloration, cracking, burnt wires — each problem has more than one cause. Identify the cause first, then change the material; if you do it in the reverse order, you often go through several rounds of changing material and still end up in the same place.
Ten, Lastly, Say Three Sentences
1. Photovoltaic junction boxes are selected with modified PP, passing through two mutually demanding thresholds, not just a V0. Weather resistance and flame retardancy, RTI and glow wire test—missing any one means it doesn't pass.
2. For conflicts with dual thresholds, solve them using a verification sequence, not by "meeting both fully." First, lock the three flame-retardant gates, then test for weather resistance on the established system; if it fails, adjust the light-stabilizing agent directionally or switch to a milder flame-retardant system, rather than increasing the quantity.
3. Do not force cases that exceed the PP limits. Long-term use above 150°C, extremely high CTI, or frequent outdoor exposure, or requiring metal-grade thermal shielding—these should use engineering plastics or metals. Make this clear first before discussing solutions.
The next article talks about photovoltaic inverter housings—the part about flame retardancy and CTI, the calculations are different again.
About Us
There are three things we never guess: temperature tolerance, lifespan, and dosage.
If the operating temperature is not given, don’t guess; if the service life is not given, don’t guess; if the monthly usage is not mentioned, don’t guess either. Any plan guessed will eventually need to be reworked and returned for claims.
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.
