JP2005087945A - Method for producing hollow fiber membrane - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing hollow fiber membranes, which can dry a large amount of the hollow fiber membranes at a high spinning speed continuously in a short time, while suppressing the occurrence of crushing. <P>SOLUTION: In this method, the hollow fiber membranes supplied continuously are dried by hot air or the hot air and water vapor. A drier is divided into drying chambers. The temperature of a forward side drying chamber in a drying process is not higher than the temperature of a backward side drying chamber, and the temperature of the first drying chamber is lower than the temperature of the last drying chamber. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a method for producing a hollow fiber membrane. More specifically, the present invention relates to a method for producing a hollow fiber membrane in which the hollow fiber membrane is continuously dried in-line in the hollow fiber membrane production process.

  In recent years, hollow fibers made of polymers have been developed and used for various purposes and applications. In particular, hollow fiber polymer membranes are used in various applications such as microfiltration membranes, ultrafiltration membranes, reverse osmosis membranes, gas separation membranes, nitrogen-rich membranes, oxygen-rich membranes, blood purification membranes, artificial kidneys, and artificial lungs. It has been put into practical use. These hollow fiber membranes are generally produced by wet spinning, dry spinning, dry / wet spinning, and melt spinning.

  For example, in the wet spinning method, a polymer fluid is discharged from a spinneret having a double ring structure, and is wound after solidification in a coagulation bath and washing (drying).

  In particular, with respect to a method for drying a hollow fiber membrane, various proposals have been made so far in order to prevent denaturation and crushing during drying. The main one is that the hollow fiber membrane in a wet state is replaced with a liquid having a low surface tension such as alcohol and then dried (Japanese Patent Laid-Open Nos. 55-51818 and 61-55208). No. 62-234510, JP-A-1-260012, etc.), and a method of heat-treating a wet hollow fiber membrane in an autoclave while maintaining the wet state (JP-A-6-327951), A method of performing wet heat treatment with steam while irradiating with microwaves (Japanese Patent Laid-Open No. 11-332980), and further, a drying method in which the hollow fiber membrane is heat-treated with warm water before drying to maintain the inside of the hollow fiber at a positive pressure ( JP 2002-253938), a method of adjusting the gas concentration in the drying process to a specific value or less (JP 2003-10654), and the like.

  However, replacement with alcohol has difficulties in terms of workability and installation of explosion-proof equipment, and the heat treatment method in the autoclave requires a special device called an autoclave and requires a long processing time. Therefore, it is not suitable when the hollow fiber membrane is continuously supplied. Furthermore, in the method using microwaves, it is difficult to control the microwaves according to the state of the yarn, and to concentrate the microwaves effectively on the hollow fiber membrane, and the outside of the drying device from the yarn inlet / outlet etc. When microwave leakage into the body occurs, there is a problem that the human body may be adversely affected. Also, in the method of treating with warm water before drying, the heating temperature cannot actually be raised to 90 ° C. or higher, and when the spinning speed of the hollow fiber membrane is high, the drying efficiency cannot catch up with the spinning speed, and crushing frequently occurs. . In the method of adjusting the gas concentration in the drying step to a specific value or less, it is necessary to add a special step such as introducing nitrogen gas into the step or compressing and cooling.

  An object of the present invention is to solve the above-mentioned problems of the prior art, and to dry a large amount of hollow fiber membranes continuously at a high spinning speed in a short time and with a low occurrence of crushing. It is an object of the present invention to provide a method for producing a hollow fiber membrane that enables the above.

In order to achieve the above object, the present invention adopts the following configuration. That is,
(1) In a method for producing a hollow fiber membrane by drying continuously supplied hollow fiber membranes with hot air or hot air and steam, a dryer is divided into drying chambers, and adjacent to the drying chambers. In the two chambers, the upstream drying chamber temperature is always equal to or lower than the downstream drying chamber temperature with respect to the traveling of the hollow fiber membrane, and the uppermost drying chamber temperature of the drying chambers is lower than the most downstream drying chamber temperature. A method for producing a hollow fiber membrane characterized by being low.

  (2) The method for producing a hollow fiber membrane according to (1), wherein the difference between the temperature in the most upstream drying chamber and the temperature in the most downstream drying chamber is 5 ° C. or more.

  (3) The method for producing a hollow fiber membrane according to (1) or (2), wherein the number of compartments of the dryer is 3 or more.

  (4) The method for producing a hollow fiber membrane according to any one of (1) to (3), wherein the hollow fiber membrane is heated with warm water before drying.

  (5) The method for producing a hollow fiber membrane according to any one of (1) to (4), wherein the spinning speed of the hollow fiber membrane is 30 m / min or more.

  (6) The method for producing a hollow fiber membrane according to any one of (1) to (5), wherein the method is for an artificial kidney.

  According to the present invention, it is possible to dry a large amount of hollow fiber membranes continuously at a high spinning speed in a short time with a reduced crushing rate.

  The drying chamber temperature referred to in the present invention is a temperature at the midpoint of a straight line or a curved distance from the blowout port of the dry air into the drying chamber to the suction port.

  The method of drying continuously supplied filaments or cloths using hot air or hot air and steam is a commonly used drying method. This drying method is used for drying hollow fiber membranes. When applied, the hollow fiber membrane is crushed and does not function as a hollow fiber membrane. Particularly when used as a blood purification membrane for an artificial kidney or the like, the collapse of the hollow fiber membrane becomes a serious defect. When a wet hollow fiber membrane is dried using hot air or hot air and steam, the reason for the occurrence of crushing is that the moisture inside the hollow fiber and inside the membrane rises due to the temperature rise on the outer surface of the membrane. This is thought to be because the temperature inside the hollow fiber does not rise and a negative pressure is generated because the latent heat of vaporization is lost. In order to prevent negative pressure inside the hollow fiber, there is a method of heating the hollow fiber membrane with warm water in advance as a measure before drying, and a method of increasing the speed of the air flowing into the hollow fiber as a measure during drying. Conceivable. Since the direction of air flow is opposite to the direction in which the hollow fiber moves, the higher the spinning speed, the higher the air speed accordingly.

  In the present invention, a dryer divided into a plurality of chambers is used. This is because when a temperature gradient is to be applied in one room, it is difficult to control the temperature due to the movement of hot air and moisture in the drying chamber, and the temperature is not stable.

  By making the drying temperature in the front of the hollow fiber drying process lower than the drying temperature in the rear and increasing the pressure of the air flowing into the hollow fiber, the inflow speed of the air is increased so that the inside of the hollow fiber is negatively affected. It can prevent becoming pressure. Moreover, the method of heating with warm water can also be combined as a countermeasure before drying.

  The drying temperature of the hot air is determined in consideration of the heat resistance of the film-forming polymer and the possible drying time. The drying temperature of the hot air is preferably from 90 ° C. to the glass transition temperature of the constituent polymer. When the temperature is lower than 90 ° C., the occurrence rate of crushing of the hollow fiber membrane is high, and when the temperature exceeds the glass transition point of the constituent polymer, the membrane structure is easily changed by heat. The occurrence rate of crushing can be measured with an optical microscope. The number of hollow fibers when looking at the occurrence rate of crushing is preferably 100 or more. If the number is less than 100, the reliability of the occurrence rate of crushing is low.

  In the present invention, a plurality of dryers each having a variable temperature are used in each chamber, and the temperature of the drying chamber in the front of the drying process is always set to be the same or lower than that in the rear in the adjacent drying chambers. The temperature difference is preferably 5 ° C. or more in the foremost drying chamber and the last drying chamber among all the drying chambers. More preferably, it is 20 degreeC or more. When the temperature is lower than 5 ° C., the inflow speed of air into the hollow fiber is insufficient, and the effect of the present invention does not sufficiently appear and the occurrence rate of crushing increases. For example, when it is separated into three chambers, it is set to 130 ° C., 140 ° C., and 150 ° C. from the front of the drying process. Also, settings such as 130 ° C., 130 ° C., and 150 ° C. are possible.

  The spinning speed of the hollow fiber membrane is preferably higher from the viewpoint of high productivity, and the spinning speed of the hollow fiber membrane in the present invention is preferably 30 m / min or more. If it is less than 30 m / min, the effectiveness of the present invention may not be sufficiently exhibited.

  When the hollow fiber membrane is in the form of a bundle of yarns, it is a preferable form from the viewpoint that a plurality of the hollow fiber membranes can be processed at the same time and high productivity is obtained.

  In the present invention, when the hollow fiber membrane is in a running state, that is, the hollow fiber membrane discharged from the die can be dried in a continuous process, and waste generation of the hollow fiber membrane occurs when the process is divided in the middle This is preferable because of high productivity.

  The hollow fiber membrane obtained by the production method of the present invention can also be used for blood purification membranes in water treatment (especially water purification) applications and medical applications. Further, since it can be processed in a large amount, it is also effectively used for applications such as ultrafiltration membranes and reverse osmosis membranes for normal industrial use. In particular, the hollow fiber membrane obtained by the production method of the present invention is preferably used for an artificial kidney.

  The membrane constituting polymer of the hollow fiber membrane used in the present invention is not particularly limited, but a skeleton made of a thermoplastic polymer such as polyethylene, polypropylene, polysulfone, polyethersulfone, polyvinyl alcohol, cellulose acetate, fluororesin, regenerated cellulose, polyamide, etc. It preferably has a structure.

  In particular, when the polymer has a glass transition point exceeding 150 ° C., there is little possibility that the film structure changes due to a dry atmosphere such as hot air, that is, the drying temperature can be increased without changing the membrane permeation characteristics. Can be performed at high speed. On the other hand, when a polymer having a glass transition point of about 100 ° C. or lower is used, the film structure is likely to change due to heat, so that it tends to be difficult to increase the drying speed.

  Hereinafter, it demonstrates still in detail according to an Example.

  Polysulfone (glass transition point 190 ° C.) 16 Wt%, polyvinyl pyrrolidone (K90) 2 Wt%, polyvinyl pyrrolidone (K30) 4 Wt% are added to dimethylacetamide 77 Wt%, water 1 Wt%, and heated and dissolved at 90 ° C. for 14 hours to form a film forming stock solution It was. This stock solution is discharged from an orifice type double cylindrical spinneret having an outer diameter of 0.3 mm and an inner diameter of 0.2 mm, and a mixed solution of dimethylacetamide 65 Wt% and water is discharged at a spinning speed of 40 m / min as a core liquid, After passing through a length of 350 mm, a coagulation bath filled with a solution consisting of 20 Wt% dimethylacetamide and 80 Wt% water, a water washing bath filled with water, a hot water bath at 90 ° C., wound after passing through a dryer, and a polysulfone hollow fiber membrane Got. The dryer was set at 130 ° C., 130 ° C., and 150 ° C. from the front using an apparatus separated into three chambers. Also, steam (water vapor) was used simultaneously with hot air in the two front chambers. When 100 hollow fiber membranes obtained were observed under an optical microscope, the occurrence rate of crushing was 14%.

(Comparative Example 1)
A hollow fiber membrane was obtained in the same manner as in Example 1 except that the dryer temperature was set to 150 ° C, 150 ° C, and 150 ° C from the front. When 100 hollow fiber membranes obtained were observed under an optical microscope, the occurrence rate of crushing was 19%.

(Comparative Example 2)
A hollow fiber membrane was obtained in the same manner as in Example 1 except that the dryer temperature was set to 170 ° C, 170 ° C, and 150 ° C from the front. When 100 hollow fiber membranes obtained were observed under an optical microscope, the occurrence rate of crushing was 50%.

    Table 1 shows the results of whether or not the hollow fiber membranes were crushed in Example 1, Comparative Example 1, and Comparative Example 2.

Claims (5)

In the method for producing a hollow fiber membrane by drying continuously supplied hollow fiber membranes with hot air or hot air and steam, the dryer is divided into three or more drying chambers, and the drying chambers are adjacent to each other. In the two chambers, the front drying chamber temperature in the drying process of the hollow fiber membrane is always equal to or lower than the rear drying chamber temperature, and the foremost drying chamber temperature is the last drying chamber temperature among the drying chambers. The manufacturing method of the hollow fiber membrane characterized by being lower. The method for producing a hollow fiber membrane according to claim 1, wherein the difference between the foremost drying chamber temperature and the rearmost drying chamber temperature is 5 ° C or more. The method for producing a hollow fiber membrane according to claim 1 or 2, wherein the hollow fiber membrane is heated with warm water before drying. The method for producing a hollow fiber membrane according to any one of claims 1 to 3, wherein the spinning speed of the hollow fiber membrane is 30 m / min or more. The method for producing a hollow fiber membrane according to any one of claims 1 to 4, wherein the hollow fiber membrane is for an artificial kidney.