KR100264676B1 - Manufacturing method of high density polyethylene hollow fiber separator - Google Patents

Abstract

PURPOSE: Disclosed is a preparing method of high density polyethylene hollow fiber separation membrane, which uses polyethylene of a low cost as a dilutor and controls easily the reformation of polymer using a shear stress. CONSTITUTION: The preparation method comprises (i) blending 20-95wt.% of high density polyethylene having a melt flow index of 1 to 20, 5-80wt.% of liquid paraffin or decaline as a diluter, 0-10wt.% of olefinic oligomer as an additive with a kneader under conditions of 150-250deg.C and 70-120psi; (ii) melt-spinning above mixture with an extruder (15) having a double-structured nozzle of 2mm in inner diameter; (iii) solidifying it by cooling wind of 5 to 30deg.C; (iv) inducing phase separation in a congelation bath (18) controlled between 10 and 30deg.C wherein the congelation bath is filled with liquid paraffin, hexane, soybean oil, decaline or their mixtures; and then (v) carrying out cold-elongation in the temperature range of 0 to 250% for controlling the pore size of a separation membrane.

Description

Manufacturing method of high density polyethylene hollow fiber separator

The present invention relates to a method for producing a hollow fiber-type separator by melt spinning method using a high density polyethylene and a diluent, and more specifically, to limit the spinning solution composition and spinning conditions in the manufacture of hollow fiber and to manufacture a hollow fiber separator using the same Therefore, the present invention relates to a method for producing a high-density polyethylene hollow fiber separator having a high-efficiency separation ability that improves permeability and separation selectivity.

The technology of separating liquid materials using polymer membranes has been used for a long time, and in particular, filtration membranes of flat membrane structure have been mainly used as ultrafiltration membranes or microfiltration membranes.

However, in recent years, in order to improve the permeation area, ultrafiltration membranes were manufactured in the form of hollow fibers, and since then, the scope of use has been variously expanded and the amount of use thereof has increased.

Conventional separators include polysulfone (Japanese Patent Application No. 56-54164), optical cross-linked polymer (Japanese Patent Application No. 52-136107, Japanese Patent Application No. 58-84006), fluorine-based polymer (Japanese Patent Application No. 59-166541), and cellulose acetate Various materials, such as a rose, polyamide, or polyester sulfone type, are used.

As a general hollow fiber membrane manufacturing method, a solvent exchange method using a solution spinning method is mainly used. This is because the polymer is dissolved in a solvent together with a pore-forming agent and spun by dry or dry-wet spinning method, so that the solvent and the non-solvent are exchanged in the non-solvent to form micropores. The same structure (finger like structure) is formed to form an asymmetrical film or the same symmetrical film may be formed the same as the outside.

Therefore, in order to improve permeability and separation selectivity, the permeation resistance should be minimized while minimizing the thickness of the separator as long as it can withstand the operating pressure in the hollow fiber membrane. As one of these methods, a separation membrane (Korean Patent Publication No. 92-1258), which forms a buffer layer between the active layer and the macroporous support layer, has been developed, but it is used in the spinning solution for polymer, cycle pore former, secondary pore former, inorganic salt and interface. Since the active agent is contained and these components act as factors, it is difficult to select the spinning solution and process conditions for optimal process control. In addition, the use of expensive polymers such as polysulfone, as well as four or more chemicals, the secondary wastewater is generated, and problems such as economic and environmental friendliness in the manufacturing process, and improves the interfacial properties of the hollow fiber membrane Additives such as surfactants used for the purpose of being washed by industrial water and household water to be treated need to pay attention to the effects of additives.

When using cellulose acetate or polyamide membranes in the process of treating water or wastewater, the heat resistance of the membranes is not good and the high temperature treatment process is difficult, and when polysulfone membranes are used, the chemical resistance of the membranes is not good. In the industrial wastewater treatment process, there is a concern that the membrane is damaged, and when the membrane of the fluorine-based polymer is used, the fluorine-based polymer does not dissolve in a conventional solvent. In addition, the contamination of solid components in the waste water adhered to the surface of the separator has been pointed out as a problem to be solved.

Even in the method of forming the membrane, the conventional solution spinning method is not an environmentally friendly process due to the pollution caused by the solvent and non-solvent used in the manufacturing process. Because of this configuration, it is pointed out that various problems such as high cost for separation and difficulty in recycling, high cost of components such as polymer, solvent, and non-solvent are high. In addition, when the separator is used in a system for treating drinking water, it is essential to examine the hazards to humans of soluble additives such as surfactants.

Accordingly, it is an object of the present invention to provide a method for producing a separator that can improve performance by changing spinning conditions without additives, having excellent properties such as heat resistance and chemical resistance, and having low manufacturing cost.

Still another object of the present invention is to provide a membrane having a wide range of applications, excellent permeability and separation selectivity, and a low-cost separation membrane by using the above-described method.

In order to achieve the above object as well as another object that can be easily expressed in the present invention, a high-density polyethylene having excellent heat resistance and chemical resistance is used as a material of the separator, and a relatively low-cost polyethylene is mixed with a diluent in a solid state. It is not only solved the conventional problems by supplying in the extruder and melting after spinning at high temperature and high pressure, but also unlike the solution spinning method which is spun in the state with little viscosity, it is easy to induce deformation such as orientation of polymer chains by external shear stress. It improves the performance of the membrane and adjusts the permeability and separation selectivity by phase separation behavior and stretching, minimizing the thickness of the membrane and allowing porosity within the range to allow pressure resistance and durability by simply changing the spinning and stretching conditions without the pore former. I was able to maximize the density .

1 is a partially cutaway front view of the high temperature high pressure kneader used in the membrane production of the present invention,

2 is a schematic manufacturing process diagram of the separator of the present invention.

* Explanation of symbols for main parts of the drawings

10 high temperature and high pressure kneader 11: stirring rod

12: high temperature and high pressure bath 13: pressure regulator

14: nozzle 15: extruder

16: nitrogen gas inlet 17: spinning nozzle

18: coagulation tank 19: water washing tank

20: winding and drawing machine

Hereinafter, the present invention will be described in more detail with reference to the accompanying drawings.

FIG. 1 is a partially cutaway front view of a high temperature high pressure kneader used in manufacturing a separator of the present invention, and FIG. 2 is a schematic drawing of a separator manufacturing process of the present invention.

In the manufacturing method of the high-density polyethylene hollow fiber membrane of the present invention by using a double-pipe blow molding nozzle, using a spinning solution consisting of a high-density polyethylene, a diluent and an additive melt-spun, but solidified in a coagulation tank after spinning to induce phase separation And stretching to adjust the size of the micropores.

The spinning stock solution is one in which 0 to 10% by weight of an additive is added to a mixture consisting of 20 to 95% by weight of polyethylene and 5 to 80% by weight of a diluent.

In the present invention, polyethylene of the spinning solution is a compound having a repeating unit represented by the following structural formula (I) and can be used by adjusting the molecular weight according to the process.

The high-density polyethylene used in the present invention is put into a heating cylinder of a MI index (melt flow indexer (test apparatus)) by molecular weight and extruded in a thin hole of the cylinder for 10 minutes under heating and pressing according to the resin. It refers to the ratio of the weight (g / 10min), and it is preferable to grind the polymer in which the thermoplastic resin in the molten state is controlled to 1 to 20 and grind the polymer to be used in powder form. If it is less than the melt spinning is difficult, if it exceeds 80% by weight, the pore formation by stretching becomes difficult.

Diluents can be used as long as they are miscible with polyethylene, but liquid paraffin or decalin are preferred. If the amount is more than 80% by weight, melt spinning is difficult, and if less than 20% by weight, pore formation due to stretching is difficult. Lose.

In addition, the additive serves to form the pores of the entire membrane to a certain size, and because the fine pores are formed in the polymer dense area, the overall pore density is improved to improve the permeation performance. The additive may also be used as long as it is miscible with polyethylene, but an olefin oligomer is preferable, and if the amount of use exceeds 10% by weight based on the total amount of polyethylene and the diluent, the durability of the hollow fiber separator manufactured may be reduced. .

Because the degree of pore formation during heat-induced phase separation is different due to the miscibility between additives, diluents, and polyethylene, the type and content ratio control are important factors to improve selectivity.

The spinning material should be uniformly mixed in the molten state, so that the additives of 0 to 10% by weight of the mixture of 20 to 95% by weight of polyethylene and 5 to 80% by weight of the diluent are controlled at 150 to 250 ° C and 70 to 120 psi. After kneading in a high temperature and high pressure kneader (10), it was powdered. The high temperature and high pressure kneader 10 is composed of a stirring rod 11, a high temperature and high pressure tank 12, a pressure regulator 13, a nozzle 14, etc., so that homogeneous mixing between the additive, the diluent, and polyethylene is possible. Changes in the structure may be easily inferred by those skilled in the art.

The powdered mixture is melted in the extruder 15 and quantitatively discharged into a gear pump (not shown), which is a precision melt pump, and passed through a spinneret 17 to make hollow fiber, 2 to 20 sccm. Nitrogen gas injection to maximize the effect. Since gas injection acts on the blow molding, the thickness of the hollow fiber membrane varies depending on the injection amount and the injection method, thereby affecting the permeation amount. In general, when the amount of nitrogen gas is increased, the thickness of the separator decreases and the permeation rate increases, but when the injected nitrogen plays a role of activating the shear normal stress acting perpendicular to the radial direction, sometimes the density increases in the direction perpendicular to the fiber axis. It also has the effect of sealing the pores and reducing the thickness of the hollow fiber membrane.

Solution spinning, which produces hollow fibers by minimizing rheological phenomena by using a solvent, is difficult to expect improvement of physical properties due to morphology in addition to the inherent properties of polymers. Factors having various physical properties can be obtained by factors in the process. In addition, in melt spinning, the polymer viscosity in the molten state is not only very sensitive to temperature but also very high in viscosity so that the structure of the fiber can be controlled by various process factors. In the present invention of melt spinning using a diluent, phase separation is induced by cooling wind or temperature drop using a coagulation bath during spinning of the melt, so that the rheological properties and cooling wind of the melt are oriented by a radial external force at a predetermined viscosity or more. Temperature control of the coagulation bath is an important factor in the structure formation of the membrane, thereby controlling the separation to maximize the separation characteristics. The temperature of the spinning nozzle 16 was 140-200 degreeC.

In the conventional melt spinning, the polymer melt from the nozzle is cooled and solidified by the cooling wind, and the emulsion is treated and wound in order to protect the fiber after the freezing point and apply it to the next process. Induced in the coagulation bath to form pores by thermally induced phase separation. The temperature of the cooling wind was 5-30 degreeC, and the temperature of the coagulation tank was 10-30 degreeC. As the coagulating solution of the coagulation bath, liquid paraffin, hexane, soybean oil, decalin and the like are used alone or in combination.

On the other hand, in solution spinning, the solvent and pore-forming agent present in the mixed system prepared during the hollow fiber membrane production are diffused and extracted from the coagulation bath after spinning, and the micropore size is determined by this speed. However, in the present invention, the pore formation is not the main phenomenon that the diluent is extracted from the coagulation bath or the diffusion phenomenon is not the main phenomenon, and the effect is different depending on the type and the temperature difference of the coagulation bath such as liquid paraffin, hexane, soybean oil, and decalin used as the coagulation solution However, the heat induced phase separation due to the temperature difference of the melt and the fine exchange by diffusion into the coagulation tank of the diluent are performed.

In the present invention, the size of the micropores was adjusted by the cold drawing method. The melt-spun hollow fiber membrane is subjected to phase separation according to the mixing ratio of the polymer, the diluent and the additive, the molecular weight, the extrusion and the cooling temperature of the polymer during the solidification process after extrusion, and forms a fine defect in the crystallization process. Cold drawing of the hollow fiber membrane with these defects according to the draw ratio induces or develops micropores. The defects in the mixed system are first deformed in the polymer lean region by external force, and then the stress is concentrated in the polymer dense region. Because it is delivered. Therefore, cold drawing was drawn at a cold drawing ratio of 0 to 250% to induce the formation of micropores that can improve the permeability and selectivity.

As described above, the present invention is melt spinning using a spinning solution having a new composition using a diluent and an additive, and thus, unlike conventional separators, permeability and selectivity can be controlled by a process.

The following examples illustrate the invention in more detail, but do not limit the scope of the invention.

Example 1

40% by weight of high density polyethylene (manufactured by Honam Petroleum Co., Ltd., 5000s) and 60% by weight of liquid paraffin (density; 0.8 to 0.9) as a diluent were mixed at 200 ° C. and 110 psi for 4 hours to prepare a mixture, and then powdered. The mixture was spun at a speed of 10 rpm at an nozzle temperature of 166 ° C. in an extruder having a hollow nozzle of 2 mm 4/4 mm. The temperature of the cooling air and the liquid paraffin coagulation bath was adjusted to 25 ° C. After the winding, the separator was cut to a predetermined length, immersed in a 20 ° C. water bath composed of hexane for 24 hours to remove the diluent, dried and cold drawn. The stretched hollow fiber was modularized to evaluate water permeability and solute rejection.

The water permeability was measured in-to-out by increasing the water pressure from 2 atm to 6 atm using pure water having a resistivity of 15.0 MΩ.cm at 25 ° C., and the solute rejection capacity was 2000, 8500, Dissolve 10000, 20000 polyethylene glycol (PEG) in a 1wt% aqueous solution, adjust the inflow to 2 or 3 atm, filter at 25 ° C, and measure by gel filtration chromatography. When compared with the equivalent effect was more than.

Example 2

52 wt% of high density polyethylene (LG Chemical Co., Ltd., ME6000) and 48 wt% of liquid paraffin (density; 0.8 to 0.9) were used as the diluent, and the nozzle temperature in the extruder was 164 ° C and spun at a speed of 12 rpm. Except for 160% cold drawing, the membrane was modularized in the same manner as in Example 1, and the water permeability and solute excretion were evaluated in the same manner as in Example 1. As a result, the membrane had an effect equal to or higher than that of the conventional product. .

Example 3

A mixture was prepared by mixing 50% by weight of high density polyethylene (LG Chemical, ME6000), 47% by weight of liquid paraffin (density; 0.8 to 0.9) with a diluent, and 3% by weight of an olefinic additive at 180 ° C and 110psi for 4 hours. After the powdering, the nozzle temperature in the extruder was 170 ℃, spun at a speed of 15rpm, and the membrane was modularized in the same manner as in Example 1 except that the cold drawing is 200% and the same method as in Example 1 As a result of evaluating water permeability and solute rejection, there was an equivalent or more effect in comparison with the conventional product.

Example 4

In the same manner as in Example 1, but the separation membrane was prepared by adjusting the temperature of the coagulation bath to 10 ~ 30 ℃ or by changing the coagulation liquid to hexane, soybean oil or decalin at 25 ℃ and evaluated the water permeability and solute rejection As a result, a separator with satisfactory performance was obtained.

As described above, in the present invention, high-density polyethylene having excellent heat resistance and chemical resistance is used as a material of the separator, and a relatively low-cost polyethylene is supplied into the extruder in a solid state in a state mixed with a diluent, melted at high temperature and high pressure, and then spun. In addition to solving the conventional problems, unlike the solution spinning method radiated in the state of little viscosity, it is easy to induce deformation such as the orientation of the polymer chains by external shear stress, thereby improving the performance of the membrane, and improving permeability and separation selectivity. By controlling the phase separation behavior and stretching, it was possible to minimize the thickness of the membrane and maximize the pore density within the range to allow pressure resistance and durability by simply changing the spinning and stretching conditions without the pore former.

Claims (1)

20 to 95% by weight of high density polyethylene having a MI value of 1 to 20, and 5 to 80% by weight of liquid paraffin or decalin as a diluent, and an olefin oligomer having 0 to 10% by weight based on the total amount of the high density polyethylene and the diluent as an additive. After powdering by mixing with a high temperature and high pressure kneader adjusted to ~ 250 ℃, 70 ~ 120 psi, and melt spinning using an extruder having a hollow tube nozzle of a double pipe structure of an inner diameter of 2mm or more, after cooling the cooling wind of 5 ~ 30 ℃ Solidified and coagulated with a coagulating solution of liquid paraffin, hexane, soybean oil or decalin alone or mixed in a coagulation bath adjusted to a temperature of 10 to 30 ° C. to induce phase separation, and cold drawing to 0 to 250% Method for producing a high density polyethylene hollow fiber membrane, characterized in that the size is adjusted.