Waterproof and moisture permeable polyethylene film and preparation method thereof

A waterproof and moisture-permeable membrane and polyethylene technology, applied in the field of waterproof and moisture-permeable membrane materials, can solve the problems of pore size stability and poor waterproof performance, and achieve excellent hydrostatic pressure resistance, low production cost, and good moisture permeability. Effect

Inactive Publication Date: 2019-03-26

UNIV OF SCI & TECH OF CHINA

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AI-Extracted Technical Summary

Problems solved by technology

However, the final film product has poor performance in terms of pore size stability an...

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Abstract

The invention provides a waterproof and moisture permeable polyethylene film and a preparation method thereof. The method comprises the following steps: S1, mixing a polyethylene raw material and white oil, performing melt extrusion, casting and cooling to obtain a cast oil film, wherein the weight-average molecular weight of the polyethylene raw material is 600000-800000, and a mass ratio of thepolyethylene raw material to the white oil is 1:(1.5-2.5); S2, heating the cast oil film to 90-110 DEG C, performing asynchronous bidirectional stretching, and performing heat setting and cooling so as to obtain a bidirectional stretched oil film, wherein a longitudinal stretching ratio of bidirectional stretching is 3-5, and a transverse stretching ratio of bidirectional stretching is 5-8; and S3, performing ultrasonic extraction on the bidirectional stretched oil film, wherein the extraction agent used for ultrasonic extraction is normal hexane or dichloromethane; and drying the extracted film, thereby obtaining the waterproof and moisture permeable polyethylene film. The waterproof and moisture permeable polyethylene film disclosed by the invention has excellent waterproof property andexcellent moisture permeability, and can be applied to the fields of medical health work, protective clothing, building safety protecting and the like.

Technology Topic

DichloromethaneMedical health +8

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Examples

Experimental program(4)
Comparison scheme(1)

Example Embodiment

[0023] The invention provides a method for preparing a polyethylene waterproof and moisture-permeable membrane, which includes the following steps:

[0024] S1. The polyethylene raw material is mixed with white oil and then melted and extruded, and then cast and cooled to obtain a cast oil film; the weight average molecular weight of the polyethylene raw material is 600,000 to 800,000, and the polyethylene raw material is mixed with white oil. The mass ratio of oil is 1: (1.5~2.5);

[0025] S2. After heating the casting oil film to 90-110°C, perform asynchronous biaxial stretching, and then heat setting and cooling to obtain the biaxial stretching oil film; the longitudinal extension ratio of the biaxial stretching is 3 to 5, The rabbi is 5~8;

[0026] S3. Perform ultrasonic extraction on the biaxially oriented oil film, and the extractant used in the ultrasonic extraction is n-hexane or dichloromethane, and then dry the extracted film to obtain a polyethylene waterproof and moisture-permeable film.

[0027] The polyethylene waterproof and moisture-permeable membrane prepared by the invention has excellent waterproofness and good moisture permeability, and has excellent mechanical properties, simple process, and favorable application.

[0028] In the embodiment of the present invention, a polyethylene cast oil film is first prepared. The main process is: using a twin-screw extruder to melt and plasticize the mixture of white oil and polyethylene raw materials, and then extrude it through a die. The extruded melt is The casting roll is rapidly cooled to produce a polyethylene casting oil film.

[0029] The present invention uses high molecular weight polyethylene raw materials, and its weight average molecular weight is 600,000 to 800,000. The present invention does not have special restrictions on the density, structure, etc. of the polyethylene raw material, and conventional commercial products can be used. In the embodiment of the present invention, the high-molecular-weight polyethylene raw material and white oil are uniformly mixed in proportion; the high-boiling, hard-to-volatile solvent of the white oil is beneficial to obtain a waterproof and moisture-permeable microporous membrane with uniform pores. The mass ratio of the polyethylene raw material to the white oil is 1: (1.5 to 2.5), preferably 1: (1.5 to 2). In addition, in order to delay the aging of the waterproof and moisture-permeable membrane during application, the present invention also preferably adds a certain amount of antioxidant to the raw material. The present invention has no special restrictions on the specific selection of the antioxidant, and preferably includes one or more of dibutyl hydroxytoluene (BHT) and tert-butyl hydroquinone (TBHQ), and more preferably is added into polyethylene BHT type antioxidant with 0.1-0.8% raw material quality.

[0030] After the polyethylene solution is obtained by mixing, the present invention preferably further includes: preheating the polyethylene solution. The embodiment of the present invention can be preheated to 90-110°C, preferably 95-105°C in the premixing kettle, and the preheating time can be 1h. Then the present invention is plasticized and melted by an extruder, and then extruded through a die. The working temperature of the extruder and the die is preferably 220-235°C, more preferably the melting temperature is 230-235°C. In the embodiment of the present invention, the extruded melt is rapidly cooled on the casting roll, and the polyethylene and white oil phase separate during the cooling process; the casting cooling temperature, that is, the working temperature of the casting roll may be 5~35℃, preferably 20~30℃, to prepare polyethylene casting oil film.

[0031] Then, in the embodiment of the present invention, the obtained polyethylene cast oil film is fixed on a biaxial stretching device and heated to 90-110°C, preferably 95-105°C, and asynchronous biaxial stretching is performed at this temperature. The predetermined stretching method stretches the cast oil film to a certain longitudinal and transverse stretch ratio, and then heat-sets and cools to obtain a biaxially stretched oil film.

[0032] The asynchronous biaxial stretching method of the present invention is first longitudinal stretching and then transverse stretching, and the biaxial stretching device can be a self-made film biaxial stretching device or other devices that can achieve biaxial stretching; The concept of "is specifically the ratio of the length of one side of the film after stretching to the initial length. In the biaxial stretching of the present invention, the longitudinal stretch ratio (longitudinal stretch ratio) is 3 to 5, and the transverse stretch ratio is 5 to 8. The longitudinal stretching rate of the biaxial stretching is preferably 1 to 2 mm/s, and the transverse stretching rate is preferably 1 to 5 mm/s. In some specific embodiments of the present invention, the longitudinal ratio is 5 and the transverse ratio is 8.

[0033] In the embodiment of the present invention, the biaxially stretched polyethylene cast oil film is heat-set, and then cooled to room temperature to prepare the biaxially stretched oil film. The heat setting and cooling are technical means well known to those skilled in the art, and the present invention is not particularly limited. The temperature of the heat setting is preferably 90 to 110°C, more preferably 95 to 105°C; after heat setting for 2 to 3 minutes, it is only required to cool to room temperature.

[0034] In the embodiment of the present invention, the biaxially stretched oil film obtained in the above steps is fixed on an extraction device, the extraction device is placed in an ultrasonic instrument containing an extractant for ultrasonic extraction, and then the extracted film is dried to obtain a polyethylene waterproof Breathable membrane.

[0035] In the present invention, the polyethylene cast oil film is first biaxially stretched, and then the volatile extractant n-hexane or dichloromethane, preferably n-hexane is used to extract the white oil in the oil film, and the size of the film is kept unchanged during extraction. A polyethylene waterproof and moisture-permeable microporous membrane with uniform pores can be obtained. The invention has no special restrictions on the extraction device, and a self-made device or other devices that can realize ultrasonic extraction can be used. In the embodiment of the present invention, the number of ultrasonic extraction can be 2 to 3 times, and each extraction is 20 to 30 minutes; then the extracted film is dried in an oven at 40 to 50° C. to a constant weight to obtain Polyethylene waterproof and breathable membrane.

[0036] The present invention provides a polyethylene waterproof and moisture-permeable membrane prepared by the above-mentioned preparation method; the thickness of the polyethylene waterproof and moisture-permeable membrane can be 5 μm-50 μm. The porosity of the polyethylene waterproof and moisture-permeable membrane is above 50%, for example, the porosity is 50-65%. The polyethylene waterproof and moisture-permeable membrane has a high porosity and a nanofiber network structure, which is similar to molten or electrospun non-woven fabric.

[0037] The present invention tests the performance of the obtained polyethylene waterproof and moisture-permeable membrane, and the results show that the hydrostatic pressure resistance of the polyethylene waterproof and moisture-permeable membrane is greater than or equal to 200KPa, and the water vapor transmission rate is 3600-4500g/m 2 · 24h. The polyethylene waterproof and moisture-permeable membrane has excellent waterproofness and good moisture permeability at the same time, which is convenient for application. In addition, the preparation method of the present invention has simple process and low cost, and is suitable for large-scale production.

Example Embodiment

[0040] Example 1

[0041] (1) Take 1.5kg polyethylene raw material (weight average molecular weight is 600,000, density is 0.96g/cm 3 ), mixed with solvent white oil 68# in a mass ratio of 1:2, add 0.5% BHT type antioxidant, and then put the obtained polyethylene solution into a preheating kettle with a temperature of 100℃ for preheating and preheating Time is 1h;

[0042] (2) Melt and extrude the preheated polyethylene solution through a twin-screw extruder at 235°C and a screw speed of 60rpm, and then pass it through a casting roll at 20°C and a roll speed of 5rpm for rapid cooling to obtain a flow Oil film

[0043] (3) Fix the casting oil film obtained above on the fixture in the biaxial stretching device, then push the fixture to the preheating furnace for preheating, the preheating temperature is 68℃, and then transport the fixture to the heating furnace, heating time 2min, temperature is 100℃;

[0044] (4) The heated casting oil film is stretched longitudinally and then transversely by asynchronous bidirectional stretching. The stretching ratio in the longitudinal stretching direction is 5, the stretching rate is 2mm/s, the stretching ratio in the transverse stretching direction is 8, and the stretching rate is 2mm/s;

[0045] (5) Heat-set the biaxially stretched cast oil film at 100°C for 3 minutes, and then cool to room temperature to obtain the biaxially stretched oil film;

[0046] (6) Fix the biaxially stretched oil film obtained in step (5) on the extraction device, and then put it into the extraction agent n-hexane for ultrasonic extraction, the extraction time is 30 min/time, and the extraction times are 3 times;

[0047] (7) Put the extracted biaxially stretched oil film into an oven at a temperature of 40° C. and dry it to a constant weight to obtain a polyethylene waterproof and moisture-permeable film with a thickness of 15 μm.

[0048] The dried waterproof and moisture-permeable membrane is subjected to waterproof performance test, moisture permeability test and SEM test. The SEM test results are as follows figure 1. Among them, the water resistance test method is the hydrostatic pressure resistance method (GB/T 4744-2013), and the moisture permeability test method is the water vapor transmission method (evaporation method) (test conditions: temperature is 38 degrees, relative humidity is 90%) .

[0049] The porosity of the waterproof and moisture-permeable membrane is 58%; the pore size distribution is 15-30nm; the longitudinal mechanical strength of the membrane is 80-120MPa, and the transverse mechanical strength is 100-150MPa; the waterproof and moisture-permeable membrane has a hydrostatic pressure resistance greater than 200KPa, Water vapor transmission rate is 4050g/m 2 · 24h.

Example Embodiment

[0050] Example 2

[0051] (1) Take 1.5kg polyethylene raw material (weight average molecular weight is 800,000, density is 0.96g/cm 3 ), mix with solvent white oil 70# in a ratio of 1:2, add 0.5% BHT type antioxidant, and then put the obtained polyethylene solution into a preheating kettle with a temperature of 100℃ for preheating, preheating time Is 1h;

[0052] (2) Melt and extrude the preheated polyethylene solution through a twin-screw extruder at 235°C and a screw speed of 60rpm, and then pass it through a casting roll at 20°C and a roll speed of 5rpm for rapid cooling to obtain a flow Oil film

[0053] (3) Fix the casting oil film obtained above on the fixture in the biaxial stretching device, then push the fixture to the preheating furnace for preheating, the preheating temperature is 68℃, and then transport the fixture to the heating furnace, heating time 2min, temperature is 100℃;

[0054] (4) The heated casting oil film is stretched longitudinally and then transversely by asynchronous bidirectional stretching. The stretching ratio in the longitudinal stretching direction is 5, the stretching rate is 2mm/s, the stretching ratio in the transverse stretching direction is 8, and the stretching rate is 2mm/s;

[0055] (5) Heat-set the biaxially stretched cast oil film at 100°C for 3 minutes, and then cool to room temperature to obtain the biaxially stretched oil film;

[0056] (6) Fix the biaxially stretched oil film obtained in step (5) on the extraction device, and then put it into the extraction agent n-hexane for ultrasonic extraction, the extraction time is 30 min/time, and the extraction times are 3 times;

[0057] (7) Put the extracted biaxially stretched oil film into an oven at a temperature of 40° C. and dry it to a constant weight to obtain a polyethylene waterproof and moisture-permeable film with a thickness of 10 μm.

[0058] See SEM test results figure 2. The porosity of the waterproof and moisture-permeable membrane is 56%; the pore size distribution is 15-30nm; the longitudinal mechanical strength of the membrane is 80-120MPa, and the transverse mechanical strength is 100-150MPa; the waterproof and moisture-permeable membrane has a hydrostatic pressure resistance greater than 200KPa, Water vapor transmission rate is 4000g/m 2 · 24h.

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PUM

Property	Measurement	Unit
Thickness	5.0 ~ 50.0	µm
Water vapor transmission rate	3600.0 ~ 4500.0	g/m2·24h
Pore size distribution	15.0 ~ 30.0	nm
tensile		MPa
Particle size		Pa
strength	10

Description & Claims & Application Information

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