CN1622971A - 纵向取向聚乙烯薄膜的制造 - Google Patents
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Abstract
公开了一种制造纵向取向聚乙烯薄膜的方法。该方法包括：使高分子量中密度聚乙烯(HMW MDPE)与线形低密度聚乙烯(LLDPE)相共混；将共混物转变成较厚的薄膜；以及使较厚的薄膜沿纵向取向形成较薄的薄膜。所制得的薄膜具有高模量，高光泽、低雾度以及较高的MD撕裂强度和落镖冲击强度。
Description
技术领域
本发明涉及单轴取向聚乙烯薄膜的制造。本发明尤其涉及由包含高分子量中密度聚乙烯(HMW MDPE)和线形低密度聚乙烯(LLDPE)的共混物来制造单轴取向聚乙烯薄膜。
背景技术
聚乙烯可分为高密度聚乙烯(HDPE，密度为0.941克/立方厘米或以上)，中密度聚乙烯(MDPE，密度为0.926-0.940克/立方厘米)，低密度聚乙烯(LDPE，密度为0.910-0.925克/立方厘米)和线形低密度聚乙烯(LLDPE，密度为0.910-0.925克/立方厘米)(见ASTM D4976-98：Standard Specification for Polyethylene Plastic Molding andExtrusion Materials)。聚乙烯(HDPE、LLDPE和LDPE)的主要用途之一是制造薄膜如用于制造杂货店用包装袋、公共机构和消费者用的金属罐内衬、商品手提袋、货物装运袋、食品包装膜、多层袋衬里、农产品包装袋、熟食品包裹膜、拉伸包装膜以及收缩包装膜。聚乙烯薄膜的主要物理参数包括撕裂强度、冲击强度、拉伸强度、劲度和清晰度。撕裂强度是按纵向(MD)和横向(TD)测定的。总撕裂强度(MD撕裂强度与TD撕裂强度的乘积)代表总撕裂性能。薄膜生产线的主要加工性能包括产量、膜泡稳定性、厚度控制(薄膜厚度变化率)，挤塑机压力和温度。
薄膜的劲度可以模量来量度。模量表示薄膜在应力下的抗变形性。模量与密度有关。密度越高模量越高。通常的LLDPE薄膜的模量为约32000磅/平方英寸，而HDPE薄膜的模量为约100000磅/平方英寸或者以上。LLDPE薄膜有较高的冲击强度，高于MD撕裂强度，而HDPE有较高的劲度和拉伸强度。当LLDPE制造者想提高密度(从而提高薄膜模量)时，他们常会遇到冲击强度和MD撕裂强度下降的情况。从历史上看，将LLDPE与HDPE相共混还没有获得“突破性”成功。由此共混物制成的薄膜虽具有较高的劲度和拉伸性能，但会牺牲冲击性能和撕裂性能。现在还没有一种快捷方法或单一树脂使薄膜能兼顾这两类性能。
近来，已经研制了一种高分子量中密度聚乙烯(HMW MDPE)(见共同未决的专利申请09/648303，2000年8月25日提出申请)。该HMW MDPE具有许多独特的性能，并为聚乙烯薄膜的改进提供了新的良机。共同未决的专利申请09/688314介绍了一种包含HWM MDPE和LLDPE的共混物。由该共混物形成的薄膜的韧度和撕裂强度较MDPE或HDPE有明显的提高，其模量较LLDPE为高。
纵向取向(MDO)早已为聚烯烃业界所知。当聚合物在单轴应力作用下发生应变时，会沿拉力方向进行取向。大多数商购MDO薄膜是通过使流延挤塑薄膜取向而制成的。当使HDPE薄膜经历MDO时，通常会提高所得薄膜的光泽、清晰度、拉伸强度、模量和阻隔性能。然而，取向薄膜的纵向撕裂强度(MD撕裂强度)和落镖冲击强度常会大大下降。
理想的是制造出具有高模量、高光泽、低雾度的、在经MDO后有较高的MD撕裂强度和落镖冲击强度的聚乙烯薄膜。
发明内容
本发明是一种制备纵向取向(MDO)聚乙烯薄膜的方法。这种取向薄膜具有高模量、高光泽、低雾度以及较高的MD撕裂强度和落镖冲击强度。该方法包括将约20重量％-约80重量％的高分子量中密度聚乙烯(HMWMDPE)与约20重量％-约80重量％的线形低密度聚乙烯(LLDPE)相共混，将共混物转变成薄膜以及使薄膜沿纵向进行单轴向取向。HMW MDPE的密度为约0.92-约0.94克/立方厘米，熔体指数(MI2)为约0.01-约0.5分克/分钟，熔体流动比率MFR为约50-约300。LLDPE的密度为约0.90-约0.93克/立方厘米，MI2为约0.5-约50分克/分钟。
具体实施方式
本发明方法包括将高分子量中密度聚乙烯(HMW MDPE)与线形低密度聚乙烯(LLDPE)相共混，将共混物转变成薄膜以及使薄膜沿纵向进行单轴向取向。
HMW MDPE的密度为约0.92-约0.94克/立方厘米。优选的密度为约0.93-约0.94克/立方厘米。优选的HMW MDPE为包含约85重量％-约98重量％的乙烯重复单元与约2重量％-约15重量％的C3-C10 α-烯烃重复单元的共聚物。适用的C3-C10 α-烯烃包括丙烯、1-丁烯、1-戊烯、1-己烯、4-甲基-1-戊烯、和1-辛烯等，以及它们的混合物。
HMW MDPE的MI2为约0.01-约0.5分克/分钟，优选为约0.01-约0.3分克/分钟，MFR为约50-约300。熔体指数(MI2)常用来量度聚合物的分子量，而熔体流动比率(MFR)常用来量度分子量分布。MI2越高表示分子量越低。MFR越高表示分子量分布越宽。MFR是高载荷熔体指数(HLMI)与MI2的比率。MI2与HLMI可按照ASTM方法D-1238测定。MI2是在190℃、2.16千克载荷下测定的。HLMI是在190℃、21.6千克载荷下测定的。HMW MDPE具有比常规HDPE或LLDPE高得多的分子量(或低得多的MI2)和宽的分子量分布(或较高的MFR)。
HMW MDPE呈多众数分子量分布。所谓“多众数分子量分布”不仅指该HMW MDPE具有至少两种不同分子量的组分，而且也指该两种组分具有相互不同的化学、结构形态。其中低分子量组分的MI2为约50-约600分克/分钟，而高分子量组分的MI2低于约0.5分克/分子量。高分子量(低MI2)组分使聚乙烯在吹膜加工中具有优良的膜泡稳定性，而低分子量(高MI2)组分能使聚乙烯具有优良的加工性能。低分子量组分优选的密度为约0.94-约0.97克/立方厘米，该密度是在常规高密度聚乙烯(HDPE)的范围之内。高分子量组分优选的密度为0.90-0.94克/立方厘米，更优选为0.91-0.94克/立方厘米，该密度与常规LLDPE类似。
共同未决的专利申请09/648303介绍了用Ziegler催化剂的多区域工艺制备HMW MDPE的方法。例如，可通过使含约85重量％-约98重量％的乙烯与约2重量％-约15重量％的C3-C10 α-烯烃的烯烃混合物在第一反应区进行聚合以制成第一聚合物，然后脱除第一聚合物中的挥发性物质，其后在第二反应区添加更多的烯烃混合物继续进行聚合来制备HMWMDPE。
LLDPE可通过Ziegler催化剂或新开发的单点催化剂来制备。Ziegler催化剂是众所周知的。适于制备LLDPE的Ziegler催化剂的实例包括卤化钛、烷氧基钛、卤化钒以及它们的混合物。Ziegler催化剂常与助催化剂如烷基铝化合物一起使用。
单点催化剂可分为金属茂和非金属茂。金属茂单点催化剂是含环戊二烯基(Cp)或Cp衍生物配体的过渡金属化合物。例如美国专利4542199介绍的金属茂催化剂。非金属茂单点催化剂包含除Cp外的配体，但仍具有与金属茂相同的催化特性。非金属茂单点催化剂可包含杂原子配体如硼芳基(boraaryl)、吡咯基、氮杂硼啉基(azaborolinyl)或喹啉基。例如，美国专利6034027、5539124、5756611和5637660所介绍的非金属茂催化剂。
LLDPE树脂通常是乙烯与5重量％-15重量％的长链α-烯烃如1-丁烯、1-己烯和1-辛烯的共聚物。LLDPE薄膜通常具有较高的抗穿刺性和撕裂强度。采用1-辛烯作为共聚单体可获得高抗冲击性和高撕裂强度。常规的1-己烯基LLDPE的性能劣于用1-辛烯制的LLDPE。然而，已研制出了能与1-辛烯基的LLDPE相媲美的具有较高性能的1-己烯基LLDPE(如见美国专利申请09/205481，1998年12月4日提出)。通常，当常规HDPE与LLDPE共混时，共混物并不同时呈现各组分的性能。然而，当LLDPE与如上所述新研制的HMW MDPE共混时，则共混物呈现出比各单一组分性能总和还要好的性能(见共同未决的专利申请09/688314)。同样，通过HMW MDPE与LLDPE共混，由该共混物制的薄膜密度可达到与目前商购LLDPE薄膜一样低，也可达到与商购MDPE薄膜一样高，于是，填补了LLDPE模量与HDPE模量之间的空档，而不会牺牲冲击性能和撕裂性能。
适用于本发明的LLDPE的密度范围为约0.9-约0.93克/立方厘米，MI2为约0.5-约50分克/分钟。
HMW MDPE与LLDPE的共混合可在溶液中或以热加工(干混)方式进行。干混是优选的。本发明的一个优点是HMW MDPE与LLDPE很容易进行共混。这两种聚合物可在室温下在金属鼓中进行滚动混合直至混合均匀。
得到的共混物包含约20重量％-约80重量％的线形低密度聚乙烯(LLDPE)。优选的是，共混物包含约30重量％-约70重量％LLDPE。任选的是，共混物可含第三种聚合物。在共混物中添加第三种聚合物既能提高产物的性能，又能降低成本。例如，添加第三种聚合物能提高薄膜的适印性或透明性。适用的第三种聚合物包括除上述规定以外的聚乙烯树脂如低密度聚乙烯(LDPE)和HDPE，聚丙烯、聚酯、丙烯酸树脂、聚乙烯醇、聚氯乙烯、聚醋酸乙烯酯、聚乙烯基醚、乙烯-醋酸乙烯酯共聚物(EVA)、乙烯-乙烯醇共聚物(EVOH)、乙烯-丙烯酸共聚物等，以及它们的混合物。第三种聚合物的添加量优选低于总共混物的50重量％。
任选的是，共混物也可包含抗氧化剂、UV-吸收剂、流动剂或其它助剂。添加剂在技术上是众所周知的。例如美国专利4086204、4331586和4812500介绍了用于聚烯烃的UV稳定剂。添加剂的添加量优选低于总共混物的10重量％。
将共混物转变成较厚的薄膜。优选的是使共混物在吹胀膜生产线上吹塑成较厚的薄膜。该工艺的加工温度优选为约150℃-约210℃。膜的厚度优选为约3密耳-12密耳，更优选为约4密耳-6密耳。
然后将该薄膜沿纵向进行单轴拉伸成较薄的薄膜。该薄膜在取向前与取向后的厚度比率称为“牵伸比”。例如，当6密耳的薄膜拉伸成1密耳时，则牵伸比为6。优选的是牵伸比是能使薄膜处于或接近于最大延伸。最大延伸是指薄膜被拉伸至再进一步拉伸就会使膜发生破裂时的牵伸膜的厚度。当纵向(MD)拉伸强度低于100％断裂伸长(ASTM D-882)时，可以说该薄膜处于最大延伸状态。正如所预期的那样，随着牵伸比的增加，薄膜的光泽提高而雾度下降。然而，令人意外地发现，当牵伸比小于3时，MD撕裂强度和落镖冲击强度下降，但当牵伸比达到薄膜的延伸接近最大时，MD撕裂强度和落镖冲击强度又会回弹上升(见表1)。
在实施MD取向时，将由吹胀膜生产线制成的薄膜加热至取向温度。优选的取向温度是玻璃化转变温度(Tg)与熔融温度(Tm)之差的约60％-约75％。例如，如果共混物的Tg为25℃，而Tm为125℃，则取向温度优选为60℃-约75℃。优选采用多个加热辊实施薄膜的加热。
然后，用夹膜辊将已加热的薄膜供入慢速牵引辊，该辊与加热辊具有相同的辊速。其后，薄膜进入快速牵引辊。快速牵引辊的速度比慢速牵引辊快2.5-10倍，该快速辊能对薄膜进行连续拉伸。
拉伸后薄膜然后进入退火加热辊，该退火辊通过使薄膜在高温下保持一定时间而对薄膜进行应力松弛。退火温度优选为约100℃-约120℃，退火时间为约1-约2秒钟。最后，薄膜通过冷却辊冷却至室温。
下面实施例只是用来说明本发明。技术熟练人员都会知道，在权利要求所规定的本发明范围和本发明的精神范围内是可有多种变化的。
实施例1-10
MD取向薄膜的制备
(a)制备HMW MDPE
催化剂是按照美国专利4464518制备的。将催化剂分散在己烷中，以得到固含量为约1.4重量％的催化剂淤浆。将催化剂淤浆(每小时0.059份)、三乙基铝助催化剂(每小时0.0033份)、己烷(每小时41.0份)、1-丁烯(每小时0.37份)和乙烯(每小时16.9份)连续地供入第一反应器。使反应器的压力和温度分别控制在140磅/平方英寸(表压)和82℃，蒸气空间中氢与乙烯的摩尔比为约3.8以形成第一聚合物。第一聚合物的MI2为220分克/分钟、密度为0.95克/立方厘米。
将第一聚合物转移至闪蒸槽内，在闪蒸槽内除去挥发性物质。然后将混合物转移至第二反应器中。将己烷(每小时42.9份)、1-丁烯(每小时1.23份)和乙烯(每小时18.6份)连续地供入第二反应器中。使反应器温度保持在77℃，蒸气空间中氢与乙烯的摩尔比为约0.05以形成MI2为约0.08分克/分钟、密度为0.94克/立方厘米的第二聚合物。
分离第二聚合物并在氮气氛下干燥。然后将干燥粉料在5％氧存在下、在适宜的稳定化混合剂存在下进行配混，以得到MI2为0.05分克/分钟、MFR为145和密度为0.94克/立方厘米的聚乙烯。
(b)HMW MDPE与LLDPE共混
将HMW MDPE与商购的LLDPE(Petrothene SelectTM Super HexeneLLDPE，Equistar Chemicals，LP)按50/50重量比相互干混。LLDPE的MI2为0.70分克/分钟，密度为0.92/立方厘米。LLDPE与HMW MDPE树脂干混并供入挤塑机。制得的共混物的MI2为0.30分克/分钟，密度为0.93克/立方厘米。
(c)共混物转变为较厚的薄膜
共混物以模口间隙为1.5毫米的200毫米模头转变为厚度为4.0密耳的薄膜。该薄膜是在注道高为六个模头直径，吹胀比(BUR)分别为3∶1(实施例1-5)和4∶1(实施例6-10)的条件下经吹塑而制成的。
(d)薄膜沿纵向进行单轴向取向
将步骤(c)制得的薄膜沿纵向拉伸成较薄的薄膜。在实施例1-5和实施例6-10中的牵伸比分别为0、2、3、4和5。当牵伸比为0时，该薄膜未经取向。薄膜的性能列于表1中。
表1
薄膜性能
| 实施例 | 牵伸比 | 吹胀比 | 光泽 | 雾度@45° | MD撕裂强度，克 | MD模量Psi | MD拉伸断裂伸长，％ | 落镖冲击强度，克 |
| 1 | 0 | 3∶1 | 7.3 | 70％ | 1100 | 54680 | 690 | 560 |
| 2 | 2 | 3∶1 | 8.3 | 64％ | 68 | 52350 | 350 | 189 |
| 3 | 3 | 3∶1 | 15 | 46％ | 29 | 53970 | 190 | 129 |
| 4 | 4 | 3∶1 | 29 | 29％ | 25 | 70570 | 110 | 128 |
| 5 | 5 | 3∶1 | 42 | 20％ | 86 | 99550 | 64 | 150 |
| 6 | 0 | 4∶1 | 6.0 | 73％ | 540 | 56590 | 620 | 552 |
| 7 | 2 | 4∶1 | 7.7 | 66％ | 45 | 56720 | 310 | 129 |
| 8 | 3 | 4∶1 | 15 | 46％ | 20 | 60050 | 184 | 95 |
| 9 | 4 | 4∶1 | 29 | 29％ | 22 | 78300 | 100 | 98 |
| 10 | 5 | 4∶1 | 40 | 22％ | 130 | 113220 | 51 | 107 |
Claims (8)
1.一种制备薄膜的方法，所述方法包括：
(a)共混
(i)约20重量％-约80重量％的密度为约0.92-约0.94克/立方厘米、MI2为约0.01-约0.5分克/分钟、MFR为约50-约300的高分子量中密度聚乙烯，该高分子量中密度聚乙烯是包含低分子量组分和高分子量组分而呈多众数分子量分布的，其中低分子量组分的MI2为约50-约600分克/分钟，密度为约0.94-约0.97克/立方厘米；与
(ii)约20重量％-约80重量％的密度为约0.9-约0.93克/立方厘米、MI2为约0.5-约50分克/分钟的线形低密度聚乙烯；
(b)使步骤(a)中得到的产物转变成薄膜；以及
(c)使步骤(b)中得到的薄膜沿纵向进行单轴向取向。
2.权利要求1的方法，其中在步骤(c)中制成的薄膜的牵伸比大于3。
3.权利要求1的方法，其中在步骤(c)中制成的薄膜的牵伸比大于4。
4.权利要求1的方法，其中线形低密度聚乙烯是乙烯与选自丙烯、1-丁烯、1-戊烯、1-己烯、1-辛烯、4-甲基-1-戊烯及它们的混合物的α-烯烃的共聚物。
5.权利要求1的方法，其中线形低密度聚乙烯是乙烯与1-己烯的共聚物。
6.权利要求1的方法，其中高分子量中密度聚乙烯的密度为约0.93-约0.94克/立方厘米。
7.权利要求1的方法，其中高分子量中密度聚乙烯的MI2为约0.01-约0.3分克/分钟。
8.权利要求1的方法制造的薄膜。
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| US10/058,894 US6613841B2 (en) | 2002-01-28 | 2002-01-28 | Preparation of machine direction oriented polyethylene films |
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| EP (1) | EP1470185B1 (zh) |
| CN (1) | CN1292019C (zh) |
| AT (1) | ATE293144T1 (zh) |
| CA (1) | CA2473805A1 (zh) |
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| CN101563225B (zh) * | 2006-12-21 | 2013-04-24 | 保瑞利斯科技公司 | 膜 |
| CN104530541A (zh) * | 2014-12-12 | 2015-04-22 | 山东嘉合塑胶制品有限公司 | 高韧性高强度peva膜 |
| CN104558760A (zh) * | 2014-12-03 | 2015-04-29 | 南宁市金装塑料彩印有限公司 | 一种高强度食品包装薄膜 |
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- 2003-01-02 CN CN03802787.9A patent/CN1292019C/zh not_active Expired - Fee Related
- 2003-01-02 CA CA002473805A patent/CA2473805A1/en not_active Abandoned
- 2003-01-02 WO PCT/US2003/000071 patent/WO2003064519A1/en not_active Application Discontinuation
- 2003-01-02 EP EP03734947A patent/EP1470185B1/en not_active Expired - Lifetime
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| CN101341208B (zh) * | 2005-12-20 | 2011-05-18 | 伊奎斯塔化学有限公司 | 高撕裂强度膜 |
| CN101563225B (zh) * | 2006-12-21 | 2013-04-24 | 保瑞利斯科技公司 | 膜 |
| CN104558760A (zh) * | 2014-12-03 | 2015-04-29 | 南宁市金装塑料彩印有限公司 | 一种高强度食品包装薄膜 |
| CN104530541A (zh) * | 2014-12-12 | 2015-04-22 | 山东嘉合塑胶制品有限公司 | 高韧性高强度peva膜 |
Also Published As
| Publication number | Publication date |
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| CN1292019C (zh) | 2006-12-27 |
| EP1470185B1 (en) | 2005-04-13 |
| DE60300501D1 (de) | 2005-05-19 |
| DE60300501T2 (de) | 2006-02-23 |
| US6613841B2 (en) | 2003-09-02 |
| CA2473805A1 (en) | 2003-08-07 |
| EP1470185A1 (en) | 2004-10-27 |
| ATE293144T1 (de) | 2005-04-15 |
| WO2003064519A1 (en) | 2003-08-07 |
| US20030144426A1 (en) | 2003-07-31 |
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