食品包装膜热封层用改性PP怎么选？答案不是"哪个牌号更软"，而是先定热封起始温度压到多少度、蒸煮等级取哪一档，再定走弹性体改性还是走 RCPP。这篇把六维工况、三条路线、十项判据与验证顺序摆清楚，并写明哪三类单子该找石化厂或膜厂。
有个做熟食软包装的技术员跟我说过两句话。
第一句："同样温度，别人的封得住，我的封不住。"
第二句："封是封住了，一装箱就顺着封口撕开。"
这两句话看着像一件事，其实是热封层（sealant layer）上最常见的两种失效：热封起始温度不够低——在产线给定的封刀温度与停留时间下没充分软化，界面没真正贴到一起；封口静强度够、抗撕抗穿不够——慢慢拉能拉住，一受力就从封口根部裂开。
普通包装膜的基材与单层膜，走石化厂膜料通道。 BOPP 基材、通用单层 CPP、芯层树脂按膜料规格由石化厂直供，改性造粒线在这类需求上没有位置。
但热封层这一侧不一样。 降起始温度、把体系做到蒸煮级、配各层热收缩、配爽滑与抗粘，这些都落在改性 PP 真正能做事的范围内。这也是本篇与 AE0（BOPP 基材方向）最大的区别。
主线只有一句：热封层的软化程度怎么定。 必须软到能封住，又不能软到一热就塌、一压就漏、一蒸就裂。
一、热封层用改性PP怎么选：把工况六个维度报齐，121℃ 那一维是一票否决
结论先说：六个维度里只有温度是一票否决的，而蒸煮温度又是温度里最硬的一条线。
| 维度 | 热封层的实际工况 | 对材料的要求 |
|---|
| 温度 | 封刀温度按材料设定（公开资料给到 CPP 层约 180–230℃）；热封起始温度：三元共聚 PP 约 108℃、弹性体改性体系可压到 102℃ 以下；蒸煮分 121℃ 与 135℃ 两档；冷链储运常在 −18℃ 档 | 软化要够、耐温要够，两条线同时要 |
| 载荷 | 热合强度与剥离力门限；堆码压力；运输跌落；内容物尖角穿刺 | 静态封得住，动态扛得住 |
| 介质 | GB/T 10004-2008 耐高温介质性用四种介质：4% 乙酸、1% 硫化钠、5% NaCl、植物油；实际还有调味液、油脂与蒸汽 | 耐介质、不分层、不起皱 |
| 寿命 | 常温长保质期货架期（蒸煮袋就是按长货架期设计的） | 封口不蠕变、助剂不迁移超标 |
| 外观 | 雾度：RCPP 常规级 ≤6%、135℃ 级 ≤8%（供应商公开 TDS 值） | 透明度与雾度同时达标 |
| 合规 | GB 4806.7-2023：总迁移 ≤10 mg/dm²、高锰酸钾消耗 ≤10 mg/kg、Pb ≤1 mg/kg、脱色阴性；GB/T 10004-2008：溶剂残留总量 ≤5.0 mg/m²、苯类不得检出 | 合规是入场券，不是加分项 |
温度之所以一票否决，原因很直白：其它维度出问题最多这批货返工，蒸煮那一关过不了，是整批报废加索赔。
二、CPP薄膜热封层三条路线怎么分工：按灌装与杀菌方式分，不按谁更好分
结论先说：三条路线不存在"谁更好"，各自对应一类灌装方式与杀菌方式。
| 路线 | 拿到什么 | 代价 |
|---|
| 弹性体（POE）改性三元共聚 PP 热封层 | 起始温度可压到 102℃ 以下（公开文献的三层共挤流延体系：三元共聚 PP + 约 12 份 POE + 爽滑剂）；韧性提升，且 POE 与三元共聚 PP 相容性好、透明度不下降 | 加量上去膜面发黏、摩擦系数上升，必须配爽滑体系；挺度略降 |
| RCPP（蒸煮级无规共聚 PP）作内封层 | 耐 121℃（普通）至 135℃（高温）；起封温度常见 ≤135℃（供应商 TDS 值） | 起封温度偏高，要更高封刀温度与更稳的温度控制；必须配各层热收缩 |
| PE / EVA 热封体系 | 起始温度更低，低温韧性有优势，成本取向清晰 | 耐温不足：公开行业资料给到 LDPE 约 110℃ 熔融、115℃ 以上降解，蒸煮下易分层与封口蠕变 |
分工按杀菌方式划：常温高速自动包装（含充气与气调、立式制袋）走弹性体改性低温热封层，要的是"低温快速热封"；要过 121℃ 及以上蒸煮走 RCPP 内封层，要的是"蒸完之后还封着"；冷藏冷冻用 PE / EVA 体系就够。
还有一层容易被忽略：热封层从来不单独存在——蒸煮袋的通行结构是内封层 + 铝箔或 PA 复合，靠的是"内层封得住 + 各层收缩配得上"。
敢否定一个常见做法：有人以为"弹性体加得越多越好封"。加量上去，膜面发黏、摩擦系数上升，自动线上打滑、黏辊、整卷粘连。公开文献给的量级是：约 12 份 POE 的体系要配 1.5 份以上爽滑剂，才能把摩擦系数压到 0.3 以下——加多了不是更好用，是更难用。
三、★ 热封层材料选型判据表：九项指标，每项都带验证方法
结论先说：这张表第四列比第一列更该先看——卡住选型的从来不是"看哪个指标"，而是"拿什么测、测到多少算过"。
| 指标 | 门限值（典型） | 验证方法 / 标准 | 常见失效 | 通行解法 |
|---|
| 热封起始温度 | 弹性体改性低温热封层 <102℃；三元共聚 PP 约 108℃；二元共聚 PP 约 135℃。公开专利文献把三元无规共聚 PP 分五档：<100 / 100–108 / 115–118 / 120–130 / >130℃ | 梯度热封 + 热封强度曲线：5–10℃ 步进，固定压力与停留时间（ASTM F2029 制样、F88 测强度；停留时间按膜厚分档 25 μm 以下 500 ms、25–64 μm 1000 ms，压力 15–30 N/cm²） | 同样温度封不住；速度一提就漏 | 换三元共聚基材或弹性体改性降起始温度 |
| 热封强度（冷却后） | 干法复合：普通级 ≥7、水煮级 ≥13、半高温蒸煮级 ≥25、高温蒸煮级 ≥35 N/15mm；挤出复合：普通级 ≥6、水煮级 ≥10；同标准的剥离力分档为 ≥0.6 / 2.0 / 3.5 / 4.5 N/15mm | GB/T 10004-2008 表 4（剥离力见表 3）；QB/T 2358 | 封口开裂、蒸煮后爆袋、层间分离 | 复核热封层厚度与封刀温度、停留时间；涂胶量与电晕处理 |
| 热粘强度（封后未冷却即受力） | 高温蒸煮级 RCPP 的公开行业资料给出 ≥1.8 N/15mm（停留 0.2 s） | ASTM F1921 | 底封"月牙形"分离、装箱即开 | 降封温或提停留时间 |
| 耐蒸煮性（耐高温介质性） | 121℃ 高压蒸煮 40 min，介质 4% 乙酸 / 1% 硫化钠 / 5% NaCl / 植物油；要求尺寸稳定、不分层、热封不开裂 | GB/T 10004-2008 | 蒸煮后起皱、破袋、漏气、异味 | RCPP 作内封层 + 各层收缩匹配 + 铝箔/PA 复合 |
| 耐高温等级 | 121℃（普通蒸煮）/ 135℃（高温蒸煮）两档；标准按普通 / 水煮 / 半高温蒸煮 / 高温蒸煮四级 | GB/T 10004-2008 分级 | 高温档下分层、封口变形 | 选高温蒸煮级内封层；135℃ 档铝箔一般取 9 μm 以上 |
| 热收缩匹配 | 各层热收缩率需匹配（RCPP 常见：纵 ≤0.8%、横 ≤1.0%，测试条件 125℃） | GB/T 10004-2008 尺寸稳定要求；供应商 TDS | 起皱、分层、封口被拉变形 | 先定内封层收缩档，再配外层结构 |
| 抗穿刺与抗冲击 | 直角撕裂力：普通级 ≥1.5 N、水煮级 ≥3.0 N、半高温与高温蒸煮级 ≥6.0 N；抗摆锤冲击能 ≥0.4–0.6 J | GB/T 10004-2008 表 5；落镖冲击 GB/T 9639.1 | 尖角穿刺、跌落破袋 | 提高内封层厚度；外层加 PA 或铝箔 |
| 食品接触合规 | 总迁移 ≤10 mg/dm²、高锰酸钾消耗 ≤10 mg/kg、Pb ≤1 mg/kg、脱色阴性；溶剂残留总量 ≤5.0 mg/m²、苯类不得检出 | GB 4806.7-2023；GB/T 10004-2008（溶剂残留） | 抽检不合格、迁移超标 | 全新料体系；助剂与胶水体系一起复核 |
| 单一材质可回收 | EVOH 阻隔层 <5% 总重可保留在聚烯烃回收流 | 行业公开资料（B 级） | 换掉铝箔后阻隔下降 | 单材多层共挤 + SiOx/AlOx 蒸镀 + 无 PVC 无炭黑 |
文字版结论：九项里 热封起始温度和热封曲线必须最先看，它决定配方能不能往下走；热合强度与剥离力是硬门限，四级分档按终端的杀菌方式对；耐高温介质性最不能跳过——验不过就是整批报废。
四、热封层材料的四类失效与根因：三条都会被归错因
结论先说：这四类失效里，有三类的第一反应都会归错因。
失效一：同样温度封不住。 根因多数不是"料变差"，而是三点之一——起始温度偏高（基材还在二元共聚甚至均聚体系上）；封刀真实温度与设定温度不一致；停留时间与产线速度不匹配。
敢否定第一个常见做法：只看熔点、不看热封起始温度，是错的。 熔点决定"能不能熔化"，起始温度决定"在产线给定的温度与时间下能不能封住"。包装线速度快、封刀停留时间短，要的是低温快速热封——靠的是软化区间，不是熔点。两个牌号熔点可以很接近，起始温度却能差十几度。
失效二：封住了，一装箱就顺着封口撕开。 包装行业管这叫"月牙形分离"，封口中部先分开，根因是热粘强度不足——封口还没冷却就在受力，此时封口层还是熔融状态，强度远低于冷却后。另一种是破坏模式不对，记录时要分清界面剥离、内聚破坏，还是基材被拉断。
失效三：蒸煮后起皱、封口变形、分层、破袋。
敢否定第二个常见做法：只测热封强度、不测热收缩匹配，是错的。 蒸煮后封口开裂往往不是强度不够，而是各层热收缩不一致——内层收缩大于外层，封口被拉变形，看着像强度问题，实际是结构问题。爆袋还有一个来源：袋内残余空气受热膨胀，靠加强度解决不了。
失效四：换了改性 PP 体系，反而在自动线上不好跑。 现象是打滑、黏辊、整卷粘连。根因在表面：弹性体加入后膜面黏性上升、摩擦系数变大，而爽滑与抗粘体系没跟上。这类问题在粒子阶段看不出来，上了自动线才暴露，所以常被记成"膜太软"。四类失效的共同点是第一反应几乎都会归错因——真正该先查的分别是起始温度与封刀温度、热粘强度、各层热收缩匹配、摩擦系数。
五、食品包装膜热封层的验证顺序：热封曲线必须排在蒸煮验证之前
结论先说：顺序错了，成本会在最后一步集中爆出来。
`
① 外观与雾度 雾度按 GB/T 2410 测
↓ 雾度超了，后面不用做
② 热封起始温度与热封曲线 梯度热封，5-10℃ 步进，固定压力与停留时间
↓ 曲线不成形、窗口过窄，退回查配方
③ 热封强度 QB/T 2358 测值，对照 GB/T 10004-2008 表 4 门限
↓ 不到门限，退回 ② 复核封刀温度
④ 蒸煮后尺寸稳定与分层 GB/T 10004-2008 耐高温介质性：121℃ 高压蒸煮 40 min，四种介质
↓ 起皱、分层、开裂，退回查热收缩匹配
⑤ 抗穿刺与抗跌落 GB/T 10004-2008 表 5 直角撕裂力与抗摆锤冲击能；落镖冲击 GB/T 9639.1
↓
⑥ 整袋灌装与运输实测 灌装温度、充气速度、堆码、跌落
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这个顺序里有两条不能动。第一，热封曲线必须排在强度之前——单点强度没有意义：起始温度附近测是低的，窗口中部测是高的，封穿温度往上又掉下来，只报一个数等于没报。第二，蒸煮必须排在抗跌落之前——它最可能一票否决，过了它再做运输侧的事，才不会白做整批。
六、反向诚实：食品包装膜热封层这三类单子该找石化厂或膜厂
结论先说：这三类需求我方能明确说"不合适"。
| 出现的情况 | 为什么改性造粒线不合适 | 该往哪走 |
|---|
| 只要通用单层 CPP 或基材膜 | 这是石化厂按膜料规格直供的通道 | 找石化厂膜料或膜厂 |
| 要求薄膜吹塑 / 流延全流程的生产配套 | 改性造粒线做的是粒子的配方与批次一致性，不是整线成膜配套 | 找膜厂 |
| 要求整幅膜的性能承诺 | 整幅膜的性能由结构与成膜工艺共同决定 | 找大装置直供或膜厂 |
反过来，我方接的是改性侧这一段：有明确起始温度要求的热封层配方（尤其低温热封方向）、有明确蒸煮等级的体系、与阻隔层的相容与收缩匹配、爽滑抗粘这类表面体系。
这条边界不难讲，难的是不漏讲。 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：CPP薄膜热封层在流延线上的一张先看再动清单
结论先说：薄膜侧的换料成本，大部分不在粒子本身，而在熔体、冷却与张力这三段。
| 要动的项 | 需要确认什么 | 不做会怎样 |
|---|
| 挤出与熔体温度 | 新改性 PP 体系的熔体温度窗口。公开文献里三层共挤流延 CPP 取 245–255℃，超出后冲击强度下降较快 | 透明度与冲击性能同时下滑 |
| 模头与流道 | 多层共挤下各层熔体黏度匹配与分配是否还成立 | 厚薄不均、层间扰动 |
| 冷却（急冷辊温度） | 温度上调会提高结晶度：公开文献给到 34℃ 时雾度增大、膜变脆，建议控制在 28℃ 以下 | 雾度上升、膜变脆、热封窗口收窄 |
| 收卷张力 | 各层收缩差异下的张力设定是否还合适 | 起皱、卷边、制袋跑偏 |
| 层间相容 | 弹性体与三元共聚 PP 的相容性；相容性差的体系透明度与光泽明显下降 | 雾度上升，外观不达标 |
| 热封窗口迁移 | 新体系的起始温度与窗口宽度（变窄＝容差变小） | 上机后才发现封不住或封穿 |
| 验证顺序 | 外观 → 热封曲线 → 强度 → 蒸煮 → 穿刺跌落 | 风险全压到最后一步集中爆出来 |
文字版结论：换料要动的是熔体温度、冷却、张力、表面体系四块，其中最该先谈的是验证顺序。跳过热封曲线直接上成品袋，等于把成本提前花出去；跳过蒸煮直接跑整批，一次失败就是整批损失。
八、一页纸汇报表：食品包装用PP热封层选型可以直接贴进 PPT
结论先说：这张表的作用是让技术员不必重新组织语言，一次会议里把方向定下来。
| 场景 | 推荐路线 | 关键指标 | 验证标准 | 需先确认的条件 |
|---|
| 常温高速自动包装（含充气 / 气调） | 三元共聚 PP + 弹性体改性的低温热封层 | 起始温度 <102℃；热封窗口宽度；摩擦系数 ≤0.3 | 梯度热封曲线；GB/T 10004-2008 表 4 | 包装机速度与封刀停留时间、内容物形态 |
| 热灌装 + 常温长货架期 | RCPP 内封层（PET/AL/RCPP 一类结构） | 剥离力 ≥4.5 N/15mm | GB/T 10004-2008 表 3、表 4 | 灌装温度、杀菌方式与时间 |
| 135℃ 高温蒸煮 | 高温蒸煮级 RCPP + 铝箔复合 | 热合强度 ≥35 N/15mm；各层热收缩匹配 | GB/T 10004-2008（含耐高温介质性） | 铝箔厚度、各层收缩档、内封层厚度 |
| 冷藏 / 冷冻 | PE / EVA 热封体系 | 低温热封与抗穿刺 | QB/T 2358；GB/T 9639.1 | 冷冻温度档、跌落高度 |
| 单一材质可回收（Mono-PP） | 全 PP 单材多层结构 + EVOH 阻隔 | EVOH <5% 总重 | 行业公开资料 | 阻隔目标值、回收流准入 |
文字版结论：五条场景线里，第一、第四条在常温侧，第二、第三条在蒸煮侧，第五条在结构侧。判断标准只有一条——客户拿这张表，能不能在一次会议里把方向定下来。
九、热封层这个件上，我们接的是哪一段
公开问题与判据：行业里常被讨论的一类现象是"封口强度测出来合格，蒸煮完还是破袋"；据公开的行业讨论，这类问题归因于热封层强度本身的比例并不高，更多出在各层热收缩不匹配、封口未冷却即受力、袋内残余空气受热膨胀这几处。判据仍写在标准里：起始温度靠梯度热封曲线定起点，热合强度与剥离力按 GB/T 10004-2008 的四级分档对门限。
行业通行解法：把三件事一起定——热封层的软化档位、体系的耐蒸煮等级、各层热收缩匹配；三者的配平关系才是这个件真正的技术难点。宁波市科隆新材料有限公司在这个方向上常供的是改性 PP 粒子里的弹性体改性低温热封方向与蒸煮级体系，按客户的起始温度要求和杀菌方式给到对应的基材档位与改性体系；配方按件调，可配合做梯度热封与蒸煮验证。
常见问答
问：现在的膜常温能封住，能不能直接拿去蒸煮？
答：不能。常温封得住只说明在你的封刀温度和停留时间下软化到位了；蒸煮要过的是另外两关——121℃ 蒸煮加四种介质后的尺寸稳定与不分层，以及蒸煮完封口还封不封得住，按 GB/T 10004-2008 的耐高温介质性验。
问：热封层是不是越软越好？
答：不是。软的目标只有一个——在产线给定的温度与停留时间下封得住。再往下软，耐蒸煮能力下降、封口受压易变形、抗穿刺变差。
问：弹性体改性和 RCPP，该按哪个方向找料？
答：按杀菌方式定。常温、高速自动包装走弹性体改性低温热封方向；要过 121℃ 及以上蒸煮走蒸煮级 RCPP 方向。
| 工况 | 关键判据 | 我方常规供应方向 |
|---|
| 常温高速自动包装（含充气 / 气调） | 热封起始温度、热封窗口、摩擦系数 | 三元共聚 PP + 弹性体改性的低温热封方向 |
| 121℃ 普通蒸煮 | 耐高温介质性、剥离力门限 | 蒸煮级方向的改性体系 |
| 135℃ 高温蒸煮 | 热合强度 ≥35 N/15mm、各层热收缩匹配 | 高温蒸煮级内封层体系 + 相容与收缩匹配 |
想提醒一句：热封层出问题，最常见的错法是先换料。封不住、蒸煮破袋、自动线打滑——每条的原因都不止一个。先定位，再换料；顺序反了，换几轮还在原地。
十、最后说三句
第一，选型的第一句话是"起始温度要压到多少度"，不是"哪个牌号软"。
第二，软化程度是配比问题：封得住之外，还要在蒸煮、堆码、穿刺三处留余量。
第三，验证顺序比验证项更重要——热封曲线排在强度之前，蒸煮排在抗跌落之前。
下一篇讲薄壁包装的另一头——微波餐盒。
关于我们
先把话讲清楚，再谈价钱。
有些单子我们宁可说"这个件我们的料不合适"，也不硬接。选型错了，便宜也是贵。基材膜走的是石化厂膜料通道，能用和不能用之间有条线，这条线我们不含糊。
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。
How to choose modified PP for the heat-seal layer of food packaging film? The answer is not "which grade is softer," but first to determine the starting temperature for heat sealing and how many degrees to press, the cooking grade to select, and then decide whether to go with elastomer modification or RCPP. This article clarifies six working conditions, three routes, ten criteria, and the order of verification, and specifies which three types of orders should be sent to petrochemical companies or film manufacturers.
A technician who works with cooked food soft packaging once said two sentences to me.
First sentence: "At the same temperature, others can seal it, but I can't."
Second sentence: 'The seal is sealed, but once you pack it in a box, it tears along the seal.'
These two sentences may seem to describe the same issue, but they actually refer to the two most common failures of the sealant layer: insufficient heat-seal initiation temperature — under the given sealing bar temperature and dwell time on the production line, it doesn't soften enough and the interface doesn't truly bond; adequate static sealing strength but insufficient tear and puncture resistance — it can hold when pulled slowly, but under stress it cracks from the base of the seal.
The substrate of ordinary packaging films and single-layer films goes through the petrochemical plant's film material channel. BOPP substrates, general single-layer CPP, and core layer resins are directly supplied by the petrochemical plant according to film material specifications, and the modified granulation line has no role in this type of demand.
But this is different on the side of the heat-seal layer. Lowering the starting temperature, making the system suitable for boiling level, matching the heat shrinkage of each layer, and balancing smoothness and anti-stickiness—these all fall within the actual capabilities of modified PP. This is also the biggest difference between this article and AE0 (BOPP substrate direction).
There is only one main point: how to determine the degree of softening of the heat-sealing layer. It must be soft enough to seal, but not so soft that it collapses when heated, leaks under pressure, or cracks when steamed.
1. How to choose modified PP for the heat-sealing layer: report all six dimensions of the operating conditions, and the 121℃ dimension is a veto.
To start with the conclusion: of the six dimensions, only temperature is a veto, and the cooking temperature is the strictest line within temperature.
| Dimension | Actual operating conditions of the heat sealing layer | Requirements for the materials |
|---|
| Temperature | The sealing temperature is set according to the material (public data indicates about 180–230℃ for the CPP layer); initial heat sealing temperature: about 108℃ for ternary copolymer PP, can be pressed below 102℃ for elastomer-modified systems; cooking is divided into two levels: 121℃ and 135℃; cold chain storage and transportation is usually at around −18℃. | Softening must be sufficient, temperature resistance must be sufficient, both lines need to be met simultaneously |
| Load | Heat seal strength and peel force threshold; stacking pressure; transport drop; piercing of contents by sharp corners | Sealed tight when static, can withstand when dynamic |
| Medium | GB/T 10004-2008 High-temperature resistant media include four types of media: 4% acetic acid, 1% sodium sulfide, 5% NaCl, and vegetable oil; in practice, there are also seasoning liquid, fat, and steam | Medium-resistant, non-laminating, wrinkle-free |
| Lifespan | Long shelf life at room temperature (the boil-in-bag is designed for long shelf life) | The seal does not creep, and the additive does not exceed migration limits |
| Appearance | Haze: RCPP regular grade ≤6%, 135°C grade ≤8% (Supplier published TDS values) | Transparency and haze meet the standards simultaneously |
| Compliance | GB 4806.7-2023: Overall migration ≤10 mg/dm², potassium permanganate consumption ≤10 mg/kg, Pb ≤1 mg/kg, decolorization negative; GB/T 10004-2008: Total solvent residue ≤5.0 mg/m², benzene not detectable | Compliance is the ticket to entry, not a bonus point |
The reason temperature can singlehandedly veto is straightforward: if there are problems in other dimensions, most of this batch will need rework; if it fails at the steaming stage, the entire batch will be scrapped and compensation will be required.
2. How to divide the three routes of CPP film heat-sealing layers: divide according to the filling and sterilization methods, not according to which is better
Conclusion first: The question of 'which is better' among the three routes does not exist; each corresponds to a type of filling method and sterilization method.
| Route | Get what | Cost |
|---|
| Elastomer (POE) Modified Ternary Copolymer PP Heat Seal Layer | The starting temperature can be reduced to below 102℃ (according to published literature on a three-layer co-extruded cast film system: ternary copolymer PP approximately 12 parts POE, slip agent); toughness is improved, and POE is compatible with ternary copolymer PP, with no decrease in transparency. | Increasing the dosage causes the film surface to become sticky and the friction coefficient to rise, so a lubricating system must be added; stiffness slightly decreases. |
| RCPP (Cooking-grade random copolymer PP) as inner sealing layer | Resistant to 121°C (normal) up to 135°C (high temperature); common peel-off temperature ≤135°C (supplier TDS value) | The initial sealing temperature is relatively high, requiring a higher sealing knife temperature and more stable temperature control; it must be equipped with heat shrinkage at each layer. |
| PE / EVA Heat Sealing System | Lower starting temperature, advantage in low-temperature toughness, clear cost orientation | Insufficient temperature resistance: Public industry data indicate that LDPE melts at about 110°C and degrades above 115°C, making it prone to delamination and seal creep under steaming. |
Division of labor by sterilization method: For room temperature high-speed automatic packaging (including gas flushing and modified atmosphere, vertical bag-making), use elastomer-modified low-temperature heat-sealing layers, aiming for "low-temperature rapid sealing"; for cooking at 121°C or above, use RCPP inner sealing layers, aiming for "still sealed after cooking"; for refrigerated or frozen use, the PE/EVA system is sufficient.
There is another layer that is easy to overlook: the heat-sealing layer never exists alone—the common structure of a cooking bag is an inner sealing layer combined with aluminum foil or PA composite, relying on 'the inner layer being sealed properly and each layer shrinking compatibly.'
Dare to challenge a common practice: some people think 'the more elastomer added, the better the sealing.' When the amount is increased, the film surface becomes sticky, the coefficient of friction rises, and there are issues like slipping on the production line, sticky rollers, and entire rolls sticking together. The quantities given in public literature are: for a system with about 12 parts POE, more than 1.5 parts of lubricant are needed to reduce the coefficient of friction below 0.3 — adding more does not make it better to use, it makes it harder to use.
3. ★ Criteria Table for Selecting Heat-Sealing Layer Materials: Nine indicators, each with a verification method
Conclusion first: In this table, the fourth column should be looked at before the first column — what always gets stuck in selection is never 'which indicator to look at,' but 'what to measure with and how much counts as passing'.
| Indicator | Threshold Value (Typical) | Verification Method / Standard | Common Failures | Common solution |
|---|
| Heat Seal Initiation Temperature | Elastomer-modified low-temperature heat-sealing layer <102℃; three-component copolymer PP about 108℃; two-component copolymer PP about 135℃. Published patent documents classify random ternary copolymer PP into five grades: <100 / 100–108 / 115–118 / 120–130 / >130℃ | Gradient heat sealing Heat sealing strength curve: 5–10℃ steps, fixed pressure and dwell time (Sample preparation according to ASTM F2029, strength testing according to F88; dwell time graded by film thickness: under 25 μm 500 ms, 25–64 μm 1000 ms, pressure 15–30 N/cm²) | The same temperature can't seal it; once the speed increases, it leaks. | Change to a terpolymer substrate or modify with elastomer to lower the starting temperature |
| Heat seal strength (after cooling) | Dry composite: Standard grade ≥7, Boiling grade ≥13, Semi-high temperature cooking grade ≥25, High-temperature cooking grade ≥35 N/15mm; Extruded composite: Standard grade ≥6, Boiling grade ≥10; The peeling force under the same standard is classified as ≥0.6 / 2.0 / 3.5 / 4.5 N/15mm | GB/T 10004-2008 Table 4 (Peel strength see Table 3); QB/T 2358 | Seal cracking, bag bursting after cooking, delamination | Review the thickness of the heat-sealing layer in relation to the sealing knife temperature and dwell time; the amount of adhesive and corona treatment |
| Hot tack strength (force applied immediately after sealing without cooling) | Public industry data for high-temperature cooking grade RCPP indicates ≥1.8 N/15mm (dwell time 0.2 s) | ASTM F1921 | Bottom-sealed 'crescent-shaped' separation, ready to open once boxed | Lower the sealing temperature or increase the dwell time |
| Steam and boil resistance (high-temperature medium resistance) | 121℃ high-pressure cooking for 40 min, medium: 4% acetic acid / 1% sodium sulfide / 5% NaCl / vegetable oil; requirements: dimensionally stable, no delamination, heat seal does not crack | GB/T 10004-2008 | Wrinkling, bag rupture, air leakage, and odor after steaming | RCPP inner sealing layer Each layer shrinkage matching Aluminum foil/PA composite |
| High temperature resistance rating | 121°C (normal cooking) / 135°C (high-temperature cooking), two levels; standard according to four levels: normal / boiling / semi-high-temperature cooking / high-temperature cooking | GB/T 10004-2008 Classification | Layering and seal deformation at high temperature settings | Choose a high-temperature cooking grade inner sealing layer; for the 135°C setting, aluminum foil is generally taken to be 9 μm or more |
| Heat shrink match | The thermal shrinkage rates of each layer need to match (Common for RCPP: longitudinal ≤0.8%, transverse ≤1.0%, test conditions 125°C) | GB/T 10004-2008 Dimensional Stability Requirements; Supplier TDS | Wrinkling, delamination, and sealing deformation | First set the shrinkage allowance for the inner sealing layer, then match the outer layer structure. |
| Puncture Resistance and Impact Resistance | Right-angle tear strength: ordinary grade ≥1.5 N, boiled grade ≥3.0 N, semi-high temperature and high-temperature boiling grade ≥6.0 N; pendulum impact energy ≥0.4–0.6 J | GB/T 10004-2008 Table 5; Dart Impact GB/T 9639.1 | Sharp corner puncture, drop and tear bag | Increase the thickness of the inner sealing layer; add PA or aluminum foil to the outer layer |
| Food Contact Compliance | Overall migration ≤10 mg/dm², potassium permanganate consumption ≤10 mg/kg, Pb ≤1 mg/kg, decolorization negative; total solvent residue ≤5.0 mg/m², no benzene detected | GB 4806.7-2023; GB/T 10004-2008 (Solvent Residue) | Sampling inspection failure, migration exceeds the limit | Completely new material system; additives and adhesive system reviewed together |
| Single material recyclable | EVOH barrier layer <5% of total weight can be retained in the polyolefin recycling stream | Industry Public Information (Category B) | Barrier decreases after replacing aluminum foil | Single material multi-layer co-extrusion SiOx/AlOx vapor deposition No PVC No carbon black |
Text version conclusion: Among the nine items, the initial temperature of heat sealing and the heat sealing curve must be checked first, as they determine whether the formulation can proceed; heat seal strength and peel force are hard thresholds, with the four-level grading aligned with the terminal sterilization method; the high-temperature resistance of the medium is the one that must not be skipped—if it fails, the entire batch is scrapped.
4. Four types of failure and root causes of heat-sealing layer materials: all three will be misattributed
Conclusion first: Among these four types of failures, the first reaction to three of them will all be to misattribute the cause.
Failure 1: The same temperature cannot seal. The root cause is often not 'material deterioration,' but one of three points: the initial temperature is too high (the substrate is still in a binary copolymer or even homopolymer system); the actual sealing knife temperature does not match the set temperature; the dwell time does not match the production line speed.
Dare to deny the first common practice: only looking at the melting point and not the heat-sealing onset temperature is wrong. The melting point determines 'whether it can melt,' while the onset temperature determines 'whether it can seal under the given temperature and time on the production line.' For high-speed packaging lines with short sealing knife dwell times, low-temperature rapid heat sealing is needed—which depends on the softening range, not the melting point. Two grades can have very close melting points, yet their onset temperatures can differ by more than ten degrees.
Failure 2: Sealed, but when packed, it tears along the seal. In the packaging industry, this is called a 'crescent-shaped separation,' where the middle of the seal separates first. The root cause is insufficient heat-sealing strength—the seal is stressed before it has cooled, at which point the sealing layer is still molten, and its strength is much lower than after cooling. Another possibility is an incorrect failure mode; when recording, it is necessary to distinguish between interfacial peeling, cohesive failure, or the base material being pulled apart.
Failure 3: Wrinkling after steaming, deformation of the seal, delamination, bag rupture.
Daring to deny the second common practice—only testing heat seal strength without checking heat shrink compatibility—is wrong. Cracking at the seal after cooking is often not due to insufficient strength, but because the heat shrinkage of each layer is inconsistent—the inner layer shrinks more than the outer layer, causing the seal to stretch and deform. It looks like a strength problem, but it is actually a structural issue. Another cause of bag bursting is residual air inside the bag expanding when heated, which cannot be solved by increasing strength.
Failure 4: After switching to a modified PP system, it actually runs poorly on the automatic line. The symptoms are slipping, sticky rollers, and full-roll adhesion. The root cause lies on the surface: after adding elastomer, the film's surface stickiness increases, and the coefficient of friction becomes higher, while the slip-enhancing and anti-adhesion systems did not keep up. This kind of problem cannot be seen at the particle stage and only appears on the automatic line, so it is often mistakenly noted as 'film too soft.' The common point of these four types of failures is that the first reaction is almost always to attribute the cause incorrectly—the things that should be checked first are the starting temperature and sealing knife temperature, thermal adhesion strength, thermal shrinkage matching between layers, and coefficient of friction.
5. Verification sequence of the heat-sealing layer of food packaging film: The heat-sealing curve must be done before cooking verification
Conclusion first: If the order is wrong, the costs will concentrate and explode in the final step.
`
① Appearance and haze Haze is measured according to GB/T 2410
↓ The fog level is too high, no need to do the rest
② Heat sealing start temperature and heat sealing curve: Gradient heat sealing, 5-10℃ increments, fixed pressure and dwell time
↓ The curve is malformed, the window is too narrow, return to check the formula
③ Heat seal strength Measured according to QB/T 2358, compared with the threshold in Table 4 of GB/T 10004-2008
↓ If below the threshold, return to ② Review the sealing temperature
④ Dimensional stability and delamination after steaming and cooking GB/T 10004-2008 High-temperature medium resistance: 121℃ high-pressure steaming for 40 minutes, four types of media
↓ Wrinkling, delamination, cracking, revert to check thermal shrinkage matching
⑤ Puncture resistance and drop resistance GB/T 10004-2008 Table 5 Right-angle tear strength and pendulum impact energy; dart impact GB/T 9639.1
↓
⑥ Full-bag filling and transportation measurements: filling temperature, inflation speed, stacking, drop
`
There are two steps in this sequence that must not be changed. First, the heat-seal curve must come before the strength test—single-point strength is meaningless: measuring near the starting temperature gives a low value, measuring in the middle of the window gives a high value, and the sealing temperature can drop again, so reporting a single number is equivalent to not reporting at all. Second, cooking must come before the drop resistance test—it is most likely to cause failure, and only after passing it should transportation-related steps be performed, so as not to waste effort on the whole batch.
6. Reverse honesty: For these three types of orders for the heat-sealing layer of food packaging films, you should contact a petrochemical plant or a film factory
Conclusion first: We can clearly say that these three types of demands are 'inappropriate'.
| The situation that occurred | Why is the modified granulation line not suitable? | Which way should I go? |
|---|
| Only general single-layer CPP or substrate film | This is the channel directly supplied by the petrochemical plant according to the membrane material specifications. | Looking for membrane materials from a petrochemical plant or a membrane factory |
| Require complete production support for film blow molding / casting process | The modified granulation line ensures the consistency of the particle's formulation and batch, not the complete line coating compatibility. | Looking for a film factory |
| Performance commitment for the entire membrane | The performance of the entire membrane is determined jointly by its structure and the film-forming process. | Looking for direct supply from large equipment or membrane factories |
On the other hand, what we are dealing with is the modified side: heat-seal layer formulations with a clear starting temperature requirement (especially for low-temperature sealing), systems with a specified cooking grade, compatibility and shrinkage matching with the barrier layer, and surface systems such as smooth and anti-sticking.
This boundary is not difficult to explain; the difficult part is explaining it without missing anything. If you take on orders forcefully, in the end, you'll have to return them with rework and claims.
7. What to move when changing materials: A checklist to look at first before handling the CPP film heat-sealing layer on the casting line
Conclusion first: The cost of material replacement on the film side is mostly not in the particles themselves, but in the three stages of melt, cooling, and tension.
| Items to move | What needs to be confirmed | What will happen if I don't do it? |
|---|
| Extrusion and Melt Temperature | Melt temperature window of the newly modified PP system. In the open literature, the melt-blown CPP for three-layer co-extrusion takes 245–255℃, and beyond this range, the impact strength decreases rapidly. | Transparency and impact performance both decline simultaneously |
| Mold Core and Runner | Does the matching and distribution of melt viscosity of each layer still hold under multi-layer coextrusion? | Uneven thickness and interlayer disturbance |
| Cooling (quenching roller temperature) | Increasing the temperature will improve crystallinity: public literature indicates that at 34°C, haze increases and the film becomes brittle, so it is recommended to keep it below 28°C. | Increase in haze, film becomes brittle, narrowing of the heat-sealing window |
| Rewinding tension | Is the tension setting still appropriate under the contraction differences of each layer? | Wrinkling, curling, bag-making deviation |
| Interlayer compatibility | Compatibility between elastomers and ternary copolymer PP; in systems with poor compatibility, transparency and gloss decrease significantly | Haze increases, appearance does not meet the standard |
| Heat-sealed window migration | The starting temperature of the new system and the window width (narrower = smaller tolerance) | Only after going on the machine did I realize it couldn't be sealed or was pierced |
| Verification order | Appearance → Heat Seal Curve → Strength → Cooking → Puncture Drop | All the risks pile up and explode at the final step |
Text version conclusion: When changing materials, the areas that need adjustment are melt temperature, cooling, tension, and surface system. Among these, the most important to discuss first is the verification sequence. Skipping the heat-sealing curve and going straight to finished bags is like spending the cost in advance; skipping cooking and running the whole batch directly means that a single failure results in the loss of the entire batch.
8. One-page report form: The selection of PP heat-seal layer for food packaging can be directly pasted into the PPT
Conclusion first: The purpose of this table is to allow the technicians to set the direction in a single meeting without having to reorganize their words.
| Scene | Recommended Route | Key indicators | Verification standard | Conditions that need to be confirmed first |
|---|
| Room temperature high-speed automatic packaging (including inflation / modified atmosphere) | Ternary Copolymer PP Elasticity-Modified Low-Temperature Heat-Sealable Layer | Starting temperature <102℃; heat sealing window width; friction coefficient ≤0.3 | Gradient thermal sealing curve; GB/T 10004-2008 Table 4 | Packaging machine speed and sealing knife dwell time, form of contents |
| Hot filling Long shelf life at room temperature | RCPP inner sealing layer (PET/AL/RCPP type structure) | Peel strength ≥4.5 N/15mm | GB/T 10004-2008 Table 3, Table 4 | Filling temperature, sterilization method and time |
| 135℃ high-temperature steaming | High-temperature cooking grade RCPP aluminum foil composite | Heat seal strength ≥35 N/15mm; thermal shrinkage of each layer is matched | GB/T 10004-2008 (including high-temperature medium resistance) | Aluminum foil thickness, shrink level of each layer, inner sealing layer thickness |
| Refrigerated / Frozen | PE / EVA Heat Sealing System | Low-temperature heat sealing and puncture resistance | QB/T 2358; GB/T 9639.1 | Freezing temperature setting, drop height |
| Single-material recyclable (Mono-PP) | All-PP single-material multi-layer structure EVOH barrier | EVOH <5% of total weight | Industry Public Information | Barrier target value, recovery stream access |
Textual Conclusion: Among the five scenario lines, the first and fourth are on the ambient side, the second and third are on the cooking side, and the fifth is on the structural side. There is only one criterion for judgment — whether the client can use this table to settle the direction in a single meeting.
9. On this heat-sealing layer part, which section are we connecting?
Public Issues and Criteria: A phenomenon commonly discussed in the industry is 'the seal strength meets the standard, but the bag still breaks after cooking.' According to public industry discussions, this type of problem is not mainly due to the proportion of the seal layer strength itself, but more due to mismatched heat shrinkage between layers, the seal being stressed before it cools, and the expansion of residual air inside the bag when heated. The criteria are still written in the standards: The starting temperature is determined by the gradient heat-seal curve, and the heat-seal strength and peel force are classified into four levels according to the thresholds in GB/T 10004-2008.
Common industry approach: Set three things together—the softening level of the heat-sealable layer, the steam-cooking resistance grade of the system, and the heat-shrink compatibility of each layer; the balance among these three is the real technical difficulty of this component. Ningbo Kolon New Materials Co., Ltd. often supplies in this direction elastomer-modified low-temperature heat-sealable modified PP particles and steam-cooking grade systems, providing corresponding substrate grades and modified systems according to the customer's starting temperature requirements and sterilization method; formulations are adjusted per component and can be used for gradient heat-sealing and steam-cooking verification.
Frequently Asked Questions
Q: The current film can seal at room temperature; can it be taken directly for steaming or boiling?
Answer: No. Being sealed at room temperature only indicates that the softening was sufficient at your sealing temperature and dwell time; cooking involves two other challenges—dimensional stability and non-lamination after cooking at 121°C with four types of media, and whether the seal can still hold after cooking. This is tested according to the high-temperature medium resistance test of GB/T 10004-2008.
Question: Is a heat-seal layer better the softer it is?
Answer: No. Soft targets have only one goal—to seal properly under the given temperature and dwell time on the production line. If made any softer, the resistance to steaming decreases, the seals are easily deformed under pressure, and puncture resistance deteriorates.
Question: For elastomer modification and RCPP, which direction should I look for materials?
Answer: It depends on the sterilization method. For room temperature, high-speed automatic packaging, follow the direction of elastomer-modified low-temperature heat sealing; for cooking at 121°C and above, follow the direction of cooking-grade RCPP.
| Operating condition | Key criterion | Our regular supply direction |
|---|
| Room temperature high-speed automatic packaging (including inflation / modified atmosphere) | Heat sealing start temperature, heat sealing window, friction coefficient | Ternary Copolymer PP: Low-Temperature Heat Sealing Direction with Elastomer Modification |
| 121℃ Normal Cooking/Steaming | High-temperature medium resistance, peel strength threshold | Modified system for cooking-grade applications |
| 135℃ high-temperature steaming | Heat seal strength ≥35 N/15mm, thermal shrinkage of each layer matched | High-temperature cooking-grade inner sealing layer system: Compatibility and shrinkage matching |
I want to give a reminder: when there is a problem with the heat-sealing layer, the most common mistake is to change the material first. Unable to seal, bags breaking during cooking, slippage on the automatic line—each issue has more than one cause. Identify the cause first, then change the material; if the order is reversed, changing the material several times will still get you nowhere.
Ten, Lastly, say three sentences
First, the first question when selecting a type is 'to what temperature should the starting temperature be reduced,' not 'which grade is softer.'
Secondly, the degree of softening is a matter of proportion: besides being able to seal, there should also be some allowance left for steaming, stacking, and piercing.
Third, the verification sequence is more important than the verification items — the heat sealing curve comes before strength, and cooking comes before drop resistance.
The next article will talk about the other end of thin-walled packaging—microwave meal boxes.
About Us
First make things clear, then talk about the price.
For some orders, we would rather say 'this piece is not suitable for our materials' than accept them forcefully. Choosing the wrong type makes even something cheap expensive. The base material film goes through the petrochemical plant's film material channel, and there is a clear line between what can and cannot be used, and we are not ambiguous about this line.
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.
