Ultrathin PE base film and preparation method thereof

Abstract

The invention relates to the technical field of PE films, in particular to an ultrathin PE base film and a preparation method thereof. The ultra-thin PE base film is obtained by sequentially carrying out the steps of shearing and melting, extruding and casting and the like on ultra-high molecular weight PE. The ultrathin PE base film has good hydrophobicity and insulativity, and is ultrathin and uniform in thickness, low in air permeability and uniform in pore structure.

Description

Technical Field

[0001] The invention relates to the technical field of PE films, in particular to an ultra-thin PE base film and a preparation method thereof. Background Art

[0002] The preparation of PE-based membranes is mainly divided into two methods: dry process and wet process. In the dry process, the polymer is first sheared and melted to form a uniform melt. Under the action of stretching, these melts form a lamellar structure. At a certain heat treatment temperature, the sheet is stretched to form slit-shaped micropores, and finally a microporous membrane is obtained after heat setting. The dry process has a relatively simple procedure, can prepare a three-layer membrane, and has less pollution. However, the dry process has the disadvantages of large thermal shrinkage and low safety. The wet process is based on the principle of thermally induced phase separation, and a twin-screw extruder is used to mix and melt the plasticizer and polyolefin resin. The molten mixture undergoes solid-liquid phase / liquid-liquid phase separation during the cooling process. After cooling into a sheet, it is heated to a certain temperature and stretched to orient the molecular chains. Then, the plasticizer is extracted from the film by volatile solvents, and finally a diaphragm with thin thickness, uniform pore size and distribution is obtained. Compared with the dry process, the base film prepared by the wet process has more advantages in thickness consistency, mechanical properties and air permeability.

[0003] In the wet base film process, the stretching process is crucial. First, it is necessary to provide sufficient heat for the sheet so that the PE molecular chains can move and align under the heat. When the oven temperature is too high, the film is prone to break during the stretching process; when the temperature is too low, the film is not heated enough, the molecular chains are not heated enough, and it is difficult to open the pore structure. Secondly, the stretching ratio affects the degree of orientation of the molecular chains. A high stretching ratio means a higher tensile strength of the base film. At the appropriate temperature, a high stretching ratio means a high stretching rate, which is conducive to improving the stretching uniformity of the base film in the oven, thereby improving the thickness consistency and air permeability uniformity of the base film. At present, the thickness of common PE wet base films is usually in the range of 7-20μm. However, with the increasing demand for lightweight and low cost, the preparation of ultra-thin base films has become a trend.

[0004] In order to overcome the defects of the prior art, the present invention provides an ultra-thin PE base film and a preparation method thereof. Summary of the invention

[0005] The object of the present invention is to provide an ultra-thin PE base film and a preparation method thereof, so as to solve the problems in the prior art.

[0006] In order to solve the above technical problems, the present invention provides the following technical solutions:

[0007] A method for preparing an ultra-thin PE base film comprises the following steps:

[0008] Step 1: The ultra-high molecular weight PE is sheared and melted, and extruded at high speed to obtain a melt; the melt is extruded and cast, and thermally induced phase separation occurs at 10-15°C, and a sheet is obtained by crystallization, and the casting speed is 3.5-5.0m / min;

[0009] Step 2: Preheating, longitudinal high-temperature stretching, and low-temperature shaping the sheet in sequence to obtain an MD stretched sheet; the longitudinal high-temperature stretching needs to complete 10-13 times of longitudinal stretching;

[0010] Step 3: Preheating, transverse stretching and shaping the sheet in sequence to obtain a TD stretched sheet; the transverse stretching needs to complete 12-20 times transverse stretching;

[0011] Step 4: placing the sheet obtained in step 3 in dichloromethane, extracting to obtain a film with a microporous structure; subjecting the film to secondary transverse stretching and heat setting, pulling and rolling, to obtain an ultra-thin PE base film; the secondary transverse stretching and heat setting requires completing 1.8-2.2 times of transverse stretching.

[0012] More optimally, in step one, the molecular weight of the ultra-high molecular weight PE is 1.6-2 million.

[0013] More optimally, in step 1, the shear melting temperature is 190-210°C; and the extrusion speed of high-speed extrusion is 190-290kg / h.

[0014] More optimally, in step 2, the preheating temperature is 85-100°C, the longitudinal high-temperature stretching temperature is 105-108°C, and the low-temperature setting temperature is 45-60°C.

[0015] More optimally, in step three, the preheating temperature is 120-128°C, and the one-time transverse stretching and low-temperature setting temperature are 114-118°C.

[0016] More optimally, in step 4, the temperature of the secondary transverse stretching and heat setting is 133-138°C; the outlet width of the secondary transverse stretching and heat setting is 5600-6000mm.

[0017] More optimally, in step 4, the sheet obtained in step 3 is placed in dichloromethane, and the dichloromethane extracts and absorbs the pore-forming agent white oil in the sheet to obtain a film with a microporous structure.

[0018] Beneficial effects of the present invention:

[0019] The present invention sequentially performs shear melting, extrusion casting, cooling casting, longitudinal high temperature stretching, transverse high temperature stretching, extraction, transverse stretching heat setting, and traction winding on ultra-high molecular weight PE to obtain an ultra-thin PE base film. The ultra-thin PE base film has good hydrophobicity and insulation, as well as ultra-thin and uniform thickness, low air permeability and uniform pore structure. These characteristics make it perform well in medical device products and outdoor sports equipment (such as band-aids, bandages, and jackets), providing good waterproof, heat dissipation, and breathable functions and a light and comfortable feel.

[0020] The present invention is characterized in that:

[0021] 1. The present invention uses ultra-high molecular weight PE as raw material, which has a high melting point, a long molecular chain and high mechanical strength, which is beneficial to improving the tensile strength of the ultra-thin sheet after transverse high-temperature stretching, so that the sheet is not easy to break in the corresponding oven.

[0022] 2. Under appropriate stretching temperature, by continuously increasing the MD pull ratio (7-10 times to 10-13 times) and TD pull ratio (10-13 times to 17-20 times), the film thickness is reduced from 3.4-4.0μm to 1.9-2.3μm.

[0023] 3. Rapidly stretching the film through high-temperature transverse stretching can ensure that the film is not easily torn during the heating and stretching process, thereby obtaining a film with uniform thickness, air permeability and uniform pore size structure.

[0024] 4. Compared with the traditional base film, the PE base film of the present invention (such as Example 4) has a thickness of only 1.92 μm, a range of 0.19 μm, an air permeability of 53.6 s / 100 mL, a range of 1.2 s / 100 mL, a contact angle of 106-110°, and a pore size mainly distributed between 33 and 40 nm, with an average pore size of 34-38 nm. It has the characteristics of ultra-thin and uniform thickness, low air permeability, good hydrophobicity, and uniform pore structure. It can be used in medical and health products and clothing products to improve their lightness and waterproof and breathable functions. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The accompanying drawings are used to provide a further understanding of the present invention and constitute a part of the specification. Together with the embodiments of the present invention, they are used to explain the present invention and do not constitute a limitation of the present invention. In the accompanying drawings:

[0026] Figure 1 is a scanning electron microscope image of Example 4 of the present invention;

[0027] Figure 2 This is a water antenna test diagram of Example 4 of the present invention;

[0028] Figure 3 is a DSC test chart of Example 4 of the present invention;

[0029] Figure 4 This is the pore size distribution diagram of Example 4 of the present invention. DETAILED DESCRIPTION

[0030] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0031] Comparative Example 1: Step 1: Ultra-high molecular weight PE is sheared and melted at 185°C and extruded at a high speed of 400 kg / h to obtain a melt; the melt undergoes thermally induced phase separation at 20°C, and a sheet is obtained by crystallization, and the casting speed is 3.7 m / min; the molecular weight of the ultra-high molecular weight PE is 1 million;

[0032] Step 2: preheating, longitudinal high-temperature stretching, and low-temperature shaping the sheet in sequence to obtain an MD stretched sheet; the longitudinal high-temperature stretching needs to complete 7 times of longitudinal stretching; the preheating temperature is 75°C, the longitudinal high-temperature stretching temperature is 95°C, and the low-temperature shaping temperature is 35°C;

[0033] Step 3: Preheating, transverse stretching and shaping the sheet in sequence to obtain a TD stretched sheet; the transverse stretching needs to complete 10 times transverse stretching; the preheating temperature is 115°C, and the transverse high temperature stretching and low temperature shaping temperature are 110°C;

[0034] Step 4: placing the sheet obtained in step 3 in dichloromethane, extracting and absorbing the pore-forming agent white oil in the sheet with dichloromethane, and obtaining a film with a microporous structure by extraction; subjecting the film to secondary transverse stretching and heat setting, and pulling and rolling, to obtain a 3.94 μm ultra-thin PE base film; the secondary transverse stretching and heat setting requires 1.89 times of transverse stretching; the temperature of the secondary transverse stretching and heat setting is 135.5°C; the outlet width of the secondary transverse stretching and heat setting is 6000 mm.

[0035] Comparative Example 2: The melt extrusion rate is changed to 350 kg / h, the transverse high-temperature stretching temperature is changed to 112°C, and the rest is the same as Comparative Example 1: Step 1: The ultra-high molecular weight PE is sheared and melted at 185°C and extruded at a high speed of 350 kg / h to obtain a melt; the melt undergoes thermally induced phase separation at 20°C, and a sheet is obtained by crystallization, and the casting speed is 3.7 m / min; the molecular weight of the ultra-high molecular weight PE is 1 million;

[0036] Step 2: preheating, longitudinal high-temperature stretching, and low-temperature shaping the sheet in sequence to obtain an MD stretched sheet; the longitudinal stretching needs to complete 7 times of longitudinal stretching; the MD preheating temperature is 75°C, the longitudinal high-temperature stretching temperature is 95°C, and the low-temperature shaping temperature is 35°C;

[0037] Step 3: Preheating, transverse stretching and shaping the sheet in sequence to obtain a TD stretched sheet; the transverse stretching needs to complete 10 times transverse stretching; the preheating temperature is 115°C, and the transverse high temperature stretching and low temperature shaping temperature are 112°C;

[0038] Step 4: placing the sheet obtained in step 3 in dichloromethane, extracting and absorbing the pore-forming agent white oil in the sheet with dichloromethane, and obtaining a film with a microporous structure by extraction; subjecting the film to secondary transverse stretching and heat setting, and pulling and rolling, to obtain a 3.48 μm ultra-thin PE base film; the secondary transverse stretching and heat setting requires 1.89 times of transverse stretching; the temperature of the secondary transverse stretching and heat setting is 135.5°C; the outlet width of the secondary transverse stretching and heat setting is 6000 mm.

[0039] Example 1: Step 1: Ultra-high molecular weight PE is sheared and melted at 195°C and extruded at a high speed of 290 kg / h to obtain a melt; the melt undergoes thermally induced phase separation at 15°C and a sheet is obtained by crystallization, and the casting speed is 3.7 m / min; the molecular weight of the ultra-high molecular weight PE is 1.7 million;

[0040] Step 2: preheating, longitudinal high-temperature stretching, and low-temperature shaping the sheet in sequence to obtain an MD stretched sheet; the longitudinal high-temperature stretching needs to complete 10 times of longitudinal stretching; the preheating temperature is 85°C, the longitudinal high-temperature stretching temperature is 105°C, and the low-temperature shaping temperature is 45°C;

[0041] Step 3: Preheating, transverse stretching and shaping the sheet in sequence to obtain a TD stretched sheet; the transverse stretching needs to complete 12 times transverse stretching; the preheating temperature is 120°C, the transverse high temperature stretching and the low temperature shaping temperature are 114°C;

[0042] Step 4: placing the sheet obtained in step 3 in dichloromethane, extracting and absorbing the pore-forming agent white oil in the sheet with dichloromethane, and obtaining a film with a microporous structure by extraction; subjecting the film to secondary transverse stretching and heat setting, and pulling and rolling, to obtain a 2.91 μm ultra-thin PE base film; the secondary transverse stretching and heat setting requires 1.89 times of transverse stretching; the temperature of transverse stretching and heat setting is 135.5°C; the outlet width of the secondary transverse stretching and heat setting is 6000 mm.

[0043] Example 2: The melt extrusion rate is changed to 225kg / h, the longitudinal high temperature stretching is changed to 13 times the longitudinal stretching, the longitudinal preheating temperature is changed to 90°C, the longitudinal stretching temperature is changed to 107°C, and the longitudinal setting temperature is changed to 55°C; the first transverse stretching preheating temperature is changed to 125°C; the second transverse stretching heat setting temperature is changed to 137°C, and the rest is the same as Example 1: Step 1: The ultra-high molecular weight PE is sheared and melted at 195°C and extruded at a high speed of 225kg / h to obtain a melt; the melt undergoes thermally induced phase separation at 15°C, and a sheet is obtained by crystallization, and the casting speed is 3.7m / min; the molecular weight of the ultra-high molecular weight PE is 1.7 million;

[0044] Step 2: preheating, longitudinal high-temperature stretching, and low-temperature shaping the sheet in sequence to obtain an MD stretched sheet; the longitudinal high-temperature stretching needs to complete 13 times of longitudinal stretching; the preheating temperature is 90°C, the longitudinal high-temperature stretching temperature is 107°C, and the low-temperature shaping temperature is 55°C;

[0045] Step 3: Preheating, transverse stretching and shaping the sheet in sequence to obtain a TD stretched sheet; the transverse stretching needs to complete 12 times transverse stretching; the preheating temperature is 125°C, the transverse high temperature stretching and the low temperature shaping temperature are 114°C;

[0046] Step 4: placing the sheet obtained in step 3 in dichloromethane, extracting and absorbing the pore-forming agent white oil in the sheet with dichloromethane, and obtaining a film with a microporous structure by extraction; subjecting the film to secondary transverse stretching and heat setting, and pulling and rolling, to obtain a 2.25 μm ultra-thin PE base film; the secondary transverse stretching and heat setting requires 1.89 times of transverse stretching; the temperature of transverse stretching and heat setting is 137°C; the outlet width of the secondary transverse stretching and heat setting is 6000 mm.

[0047] Example 3: The extrusion rate is changed to 200 kg / h; the longitudinal preheating temperature is changed to 100°C, and the longitudinal setting temperature is changed to 60°C; the first transverse stretching is changed to 15 times transverse stretching; the first transverse stretching preheating temperature is changed to 128°C; the rest is the same as Example 2: Step 1: The ultra-high molecular weight PE is sheared and melted at 195°C and extruded at a high speed of 200 kg / h to obtain a melt; the melt undergoes thermally induced phase separation at 15°C, and a sheet is obtained by crystallization, and the casting speed is 3.7 m / min; the molecular weight of the ultra-high molecular weight PE is 1.7 million;

[0048] Step 2: preheating, longitudinal high-temperature stretching, and low-temperature shaping the sheet in sequence to obtain an MD stretched sheet; the longitudinal high-temperature stretching needs to complete 13 times of longitudinal stretching; the preheating temperature is 100°C, the longitudinal high-temperature stretching temperature is 107°C, and the low-temperature shaping temperature is 60°C;

[0049] Step 3: Preheating, transverse stretching and shaping the sheet in sequence to obtain a TD stretched sheet; the transverse stretching needs to complete 15 times transverse stretching; the preheating temperature is 128°C, the transverse high temperature stretching and the low temperature shaping temperature is 114°C;

[0050] Step 4: placing the sheet obtained in step 3 in dichloromethane, extracting and absorbing the pore-forming agent white oil in the sheet with dichloromethane, and obtaining a film with a microporous structure by extraction; subjecting the film to secondary transverse stretching and heat setting, and pulling and rolling, to obtain a 1.93 μm ultra-thin PE base film; the secondary transverse stretching and heat setting requires 1.89 times of transverse stretching; the temperature of transverse stretching and heat setting is 137°C; the outlet width of the secondary transverse stretching and heat setting is 6000 mm.

[0051] Example 4: The first transverse stretching is changed to 17 times transverse stretching, and the rest is the same as Example 3: Step 1: The ultra-high molecular weight PE is sheared and melted at 195°C and extruded at a high speed of 200 kg / h to obtain a melt; the melt undergoes thermally induced phase separation at 15°C, and a sheet is obtained by crystallization, and the casting speed is 3.7 m / min; the molecular weight of the ultra-high molecular weight PE is 1.7 million;

[0052] Step 2: preheating, longitudinal high-temperature stretching, and low-temperature shaping the sheet in sequence to obtain an MD stretched sheet; the longitudinal high-temperature stretching needs to complete 13 times of longitudinal stretching; the preheating temperature is 100°C, the longitudinal high-temperature stretching temperature is 107°C, and the low-temperature shaping temperature is 60°C;

[0053] Step 3: Preheating, transverse stretching and shaping the sheet in sequence to obtain a TD stretched sheet; the transverse stretching needs to complete 17 times transverse stretching; the preheating temperature is 128°C, the transverse high temperature stretching and the low temperature shaping temperature are 114°C;

[0054] Step 4: placing the sheet obtained in step 3 in dichloromethane, extracting and absorbing the pore-forming agent white oil in the sheet with dichloromethane, and obtaining a film with a microporous structure by extraction; subjecting the film to secondary transverse stretching and heat setting, and pulling and rolling, to obtain a 1.92 μm ultra-thin PE base film; the secondary transverse stretching and heat setting requires 1.89 times of transverse stretching; the temperature of transverse stretching and heat setting is 137°C; the outlet width of the secondary transverse stretching and heat setting is 6000 mm.

[0055] Detection test:

[0056] Test instruments: Mahr thickness gauge (C1216M+P2004MA); Gurley permeability meter (4110N+4320); electronic molecular balance; microcomputer-controlled electronic universal material testing machine (CTM2010s); tensile sample size is 200*15mm, tensile rate is 250mm / min, puncture needle diameter is 1.0mm, and the tip is a spherical radius of 0.5mm; electric constant temperature blast drying oven (DHG-9423A); image measuring instrument (VMS432); the interval between the transverse thickness test points is 10cm, and the interval between the transverse permeability test points is 10cm; the porosity calculation formula is:

[0057]

[0058]

[0059]

[0060] Conclusion: In Comparative Examples 1 and 2, the preheating temperature (115°C) and stretching temperature (110°C, 112°C) of the first transverse stretching were low, resulting in frequent film breakage in the 1TD oven; since the extrusion volume of Comparative Examples 1 and 2 was relatively large, 400kg / h and 350kg / h respectively, the product thicknesses were 3.94 and 3.48μm respectively; and the MD and 1TD stretching ratios (7 times and 10 times) were relatively low, the local pore structure of the diaphragm was not opened, and the air permeability and thickness extremes were both large, with the air permeabilities being 136.9 and 116.7s / 100mL respectively, the air permeability extremes being 27.9 and 18.5s / 100mL respectively, and the thickness extremes being 1.03 and 0.86μm respectively.

[0061] The contact angle test was performed on the sample obtained in Example 4 ( Figure 2 ), the contact angle is 108.169°, indicating that the material has good hydrophobicity; by analyzing the scanning electron microscope image of Example 4 ( Figure 1 ) shows that the prepared base membrane has a normal microporous structure, without closed pores and obvious coarse crystals; by performing DSC test on the sample obtained in Example 4 ( Figure 3 ), the melting point is 148.84 ℃, indicating that the material has good thermodynamic properties; the pore size distribution diagram of the sample obtained in Example 4 ( Figure 4 ) analysis shows that the sample pore size is mainly distributed between 33-40nm, the average pore size is 35.6nm, and the bubble point pore size is 42.7nm, indicating that the pore size distribution and structure of the sample are normal.

[0062] It should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variations thereof are intended to cover non-exclusive inclusion, so that a process method article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process method article or device.

[0063] Finally, it should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art can still modify the technical solutions described in the aforementioned embodiments or replace some of the technical features therein by equivalents. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for preparing an ultra-thin PE base film, characterized in that: The following steps are involved: Step 1: The ultra-high molecular weight PE is sheared and melted, and extruded at high speed to obtain a melt; the melt is extruded and cast, and thermally induced phase separation occurs at 10-15°C, and a sheet is obtained by crystallization, and the casting speed is 3.5-5.0m / min; Step 2: Preheating, longitudinal high-temperature stretching, and low-temperature shaping the sheet in sequence to obtain an MD stretched sheet; the longitudinal high-temperature stretching needs to complete 10-13 times of longitudinal stretching; Step 3: Preheating, transverse stretching and shaping the sheet in sequence to obtain a TD stretched sheet; the transverse stretching needs to complete 12-20 times transverse stretching; Step 4: placing the sheet obtained in step 3 in dichloromethane, extracting to obtain a film with a microporous structure; subjecting the film to secondary transverse stretching and heat setting, pulling and rolling, to obtain an ultra-thin PE base film; the secondary transverse stretching and heat setting requires completing 1.8-2.2 times of transverse stretching.

2. The method for preparing an ultra-thin PE base film according to claim 1, characterized in that: In step 1, the molecular weight of the ultra-high molecular weight PE is 1.6-2 million.

3. The method for preparing an ultra-thin PE base film according to claim 1, characterized in that: In step 1, the shear melting temperature is 190-210° C.; the extrusion speed of high-speed extrusion is 190-290 kg / h.

4. The method for preparing an ultra-thin PE base film according to claim 1, characterized in that: In step 2, the preheating temperature is 85-100°C, the longitudinal high-temperature stretching temperature is 105-108°C, and the low-temperature setting temperature is 45-60°C.

5. The method for preparing an ultra-thin PE base film according to claim 1, characterized in that: In step three, the preheating temperature is 120-128°C, and the primary transverse stretching and low-temperature setting temperatures are 114-118°C.

6. The method for preparing an ultra-thin PE base film according to claim 1, characterized in that: In step 4, the temperature of the secondary transverse stretching and heat setting is 133-138° C.; the outlet width of the secondary transverse stretching and heat setting is 5600-6000 mm.

7. The method for preparing an ultra-thin PE base film according to claim 1, characterized in that: In step 4, the sheet obtained in step 3 is placed in dichloromethane, and the dichloromethane extracts and absorbs the pore-forming agent white oil in the sheet to obtain a film with a microporous structure.

8. An ultra-thin PE base film, characterized in that: Prepared according to the preparation method according to any one of claims 1 to 7.

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