JPH04187226A - Polyamide hollow yarn membrane and its production - Google Patents

Abstract

PURPOSE:To form a polyamide hollow yarn membrane with the internal structure exhibiting excellent elastic recovery and micropore forming property by wet-heat-treating a polyamide hollow yarn having 15X10<-3> to 35X10<-3> birefringence and with both ends opened while keeping the yarn tensionless. CONSTITUTION:A polyamide hollow yarn having 15X10<-3> to 35X10<-3> birefringence and with one or both ends opened is wet-heat-treated with pressurized steam or pressurized hot water while keeping it tensionless to produce a polyamide hollow yarn membrane. The obtained membrane gas 25X10<-3> to 40X10<-3> birefringence in its orientation direction, >=1.150g.cm<-3> density, >=70% elastic recovery rate at 50% elongation and >=1.0X10<-5> cm<-3>.cm<-2>.sec<-2>.cmHg<-1> nitrogen diffusibility at 50% elongation. The membrane is drawn and heat-treated, as required, to fix its internal structure and to further orient the crystal lamella. The ordinary crystalline polyamide such as nylon 6, nylon 66, nylon 12, nylon 610 and nylon 46 is exemplified as the polyamide.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a polyamide hollow fiber membrane having excellent elastic recovery properties and a method for producing the same. More specifically, the present invention relates to a highly elastic polyamide hollow fiber membrane having high orientation and high crystallinity, and a method for producing the same.

[Prior Art] Various proposals have been made for stretchable or microporous hollow fibers and methods for producing them. For example, JP-A-52-137026, JP-A-58-4810
There is a number.

These were obtained by a method that generates laminated lamellae and utilizes the reversibility of their deformation. However, only hollow fiber membranes made of polyolefin, polyoxymethylene, and polyfluorovinylidene have been produced and are known, and it is believed that the production method for polyolefins can be applied to other highly crystalline polymers. Despite this, hollow fiber membranes made of polyamide have never actually been manufactured.

When the conventional method was repeated, hollow fiber membranes could not be obtained even when the manufacturing method applied to polyolefins was applied to polyamide.

In other words, the conventional method known for manufacturing microporous hollow fiber membranes such as polyolefins is to spin hollow fibers by applying a high shear rate, annealing them under slight tension, and then stretching and heat-setting them. , a method in which hollow fibers are spun and annealed, followed by cold stretching, hot stretching and heat setting; a method in which hollow fibers are spun, drawn, annealed, then drawn and heat set;
Here, as a means of annealing, dry heat treatment using a heating roll or an oven is used. However, unlike the case of highly crystalline polymers such as polyolefin, in the case of polyamide, when ordinary dry heat treatment such as an oven is used, crystal lamellae hardly develop and a useful hollow fiber membrane cannot be obtained.

On the other hand, regarding polyamide fibers, a method of growing crystalline lamellae by high-speed spinning and treatment with a phenol solution is proposed in U.S. SP No. 351-3], No. 10. However, this known method involves processing using chemicals such as phenol, so the process is complicated, takes a long time, and is unfavorable from an environmental point of view. Therefore, residual phenol may have a large negative effect on the hollow fiber itself in the subsequent process.
For example, it accelerates the deterioration of polyamide, causing discoloration and a decrease in strength and elongation, making it difficult to obtain uniform hollow fibers.
The elastic properties were also insufficient.

[Problems to be Solved by the Invention] Therefore, the present inventors repeatedly investigated hollow fiber membranes made of polyamide, and were able to obtain a polyamide hollow fiber membrane with excellent stretchability, leading to the present invention. Ta.

An object of the present invention is to provide a polyamide hollow fiber membrane having an internal structure that exhibits excellent elastic recovery properties and microporous formation properties, and to provide a method for easily producing the polyamide hollow fiber membrane. .

Another object is to provide a new material called a hollow fiber membrane made of polyamide, and also to provide a polyamide material that can be easily made into a microporous hollow fiber membrane.

[Means for Solving the Problems] In order to achieve the above object, the present invention has the following configuration.

(1) Birefringence in the orientation direction is 25XiO-3 to 40×10
″′3, density is 1.1-50 g-cm-3 or more, 5
When the elastic recovery rate at 0% elongation is 70% or more and the nitrogen permeability is at 50% elongation, i, OXl, 0-5 cm-3.
1. A polyamide hollow fiber membrane characterized in that it has an Hg' or higher.

(2) Birefringence is i5X10'-"~35X10-
3. A method for producing a polyamide hollow fiber membrane, which comprises opening both ends or one end of the polyamide hollow fiber and subjecting it to a moist heat treatment using pressurized saturated steam or pressurized hot water while keeping the polyamide hollow fiber in a tension-free state.

Birefringence, density, elastic recovery rate at 50% elongation, as referred to in the present invention,
The nitrogen permeability is a value measured by the following method.

The measurement is carried out using birefringent biwhite light as the light source and liquid paraffin as the immersion liquid.

Density is measured at 25°C using a density gradient tube using a mixed medium of carbon ditetrachloride and toluene.

Elastic recovery rate at 50% elongation A hollow fiber with a fiber length of 20 cm was tested using a tensile tester at an initial load of 0.33 kg-mm-2 and a tensile speed of 1.
Stretch to 50% elongation (10 cm) at 0cm-m1n', then remove the weight at the same speed as the above tension speed, leave it for 2 minutes at the same gripping interval (20 cm) as at the beginning, and then again at the same speed as the above tension speed. It stretches at 0.0 and the stress is the same as the initial load. 33
Let Lcm be the elongation distance until reaching kg-mm-2. The elastic recovery rate (%) at 50% elongation is calculated using the following formula: %.

Nitrogen permeability: A small module of a microporous hollow fiber membrane bundle was made, nitrogen pressure was applied inside the hollow fibers, and the unit amount of nitrogen that permeated to the outside through the membrane was measured at 25°C.

The polyamide hollow fiber membrane of the present invention has a structure completely different from that of conventional polyamide hollow fiber membranes, and as mentioned above, it has unique birefringence, density, and 50%
It is characterized by a combination of elastic recovery rate during elongation and nitrogen permeability. That is, the hollow fiber membrane is estimated to have the following internal structure.

Crystal lamellae grown in a direction perpendicular to the axial direction are stacked, and the area between the crystal lamellae is a poor quality region with extremely low density. This structure shows almost no permeability as it is, but when stretched mechanically, the lamella deforms and the interlamellar amorphous region becomes voided, allowing air, gases such as nitrogen, and liquids such as water to pass through. In other words, the nitrogen permeability at 50% elongation is 1
゜0×10-5cm-3・cm-2・sec″2・cm
Hg-1 or higher is indicated. Furthermore, the deformation of lamellae and the creation of voids caused by mechanical stretching are reversible, and therefore the elastic recovery rate at 50% stretching is 70%.
Above, preferably 75% or more. Furthermore,
Even the birefringence, which indicates the average value of the orientation of the interlamellar amorphous region, is 25
In the other crystal lamella region, the lamination and orientation of lamellae are sufficiently developed as shown by the high degree of orientation such as X10-3 to 35×10″3, and the density is 1.150 g-C.
It has grown to such a high degree that it shows 1.155 g-cm-3 or more, preferably 1.155 g-cm-3 or more.

Polyamide hollow fiber membranes with such an internal structure are highly stretchable and also exhibit excellent stretch durability, with an elastic recovery rate of 60% or more, preferably 65% or more, at the 20th repetition of 50% stretching deformation. be able to.

The hollow fiber membrane according to the present invention is made of polyamide,
Moreover, it is unique in that it has a high degree of elastic recovery and microporous formation, and therefore has excellent properties that cannot be obtained with conventional stretchable hollow fibers such as polyolefin and polyoxymethylene. For example, since the density of the amorphous part is extremely low and the molecular chain is sufficiently relaxed, combined with the presence of hydrophilic groups, the amorphous part can absorb a large amount of water. It can exhibit unprecedented water retention.

Furthermore, since it has a polar group, it can be bonded extremely easily when making composites with various resins, rubbers, etc. Furthermore, the dyeability is also excellent.

Polyamide hollow fiber membranes with such excellent properties are
For example, in addition to applications that take advantage of high elastic recovery properties, it is also possible to utilize the fine voids to create highly water-absorbent hollow fiber membranes or highly solvent-absorbent hollow fiber membranes, or to form micropores by mechanical elongation. It can be used for separation.

Hereinafter, a method for manufacturing a polyamide hollow fiber membrane having the above-mentioned internal structure will be explained.

The main features of the present invention are (1) applying moist heat treatment using pressurized saturated steam or pressurized hot water to hollow fibers that are open at both ends or in a tension-free state, thereby growing crystal lamellae; (2) Furthermore, the birefringence of the polyamide hollow fibers subjected to the moist heat treatment is 15X10-3~
It has a degree of orientation characterized by 35X10-3.

The moist heat treatment is performed using pressurized saturated steam or pressurized hot water, and "saturated steam" here is preferably saturated steam, but near-saturated steam can also be used in some cases.

Moist heat treatment is 2.5-5.0kg-Cm-2,1-38~
It is preferable to conduct the reaction at a temperature of 160° C. in view of the characteristics of the hollow fiber membrane obtained.

If the treatment pressure is too low, the treatment will be insufficient and crystal lamella growth will not be achieved sufficiently, resulting in poor properties of the resulting hollow fiber membrane. On the other hand, if the temperature is too high, the properties of the resulting hollow fiber membranes will deteriorate, but what is worse is that the hollow fibers will begin to melt during the wet heat treatment, resulting in mutual fusion of the hollow fiber membranes.

Furthermore, the moist heat treatment must be performed with both ends or one end of the polyamide hollow fibers open and kept in a non-tensioned state, but the treatment may be performed continuously or batchwise. . In the case of a continuous type, this can be achieved by attaching multistage slits to the inlet and outlet portions of the processing cylinder and sufficiently sealing them. On the other hand, in the case of a batch method, an autoclave is used, and the treatment usually takes several minutes or more, including the time required for operation and temperature rise. When performing moist heat treatment for a relatively long period of time, an antioxidant for polyamide is added during the polymerization process to prevent thermal oxidative deterioration of polyamide.
Alternatively, it is desirable to add it during the spinning process and impregnate it into the hollow fibers, or to perform a wet heat treatment using water containing a 1L agent during water-soluble oxidation.

Polyamide hollow fibers subjected to moist heat treatment must have a degree of orientation within a specific range, which is 15X1 in terms of birefringence.
It is 0-3 to 35×10-3. The orientation condition is an important condition for imparting elastic recovery properties and micropore formation properties to the resulting hollow fibers, and hollow fiber membranes with excellent properties cannot be obtained from hollow fibers that deviate from this condition. More preferably, hollow fibers with a birefringence of 20XIO-3 to 30X10-' are provided. After achieving specific orientation conditions, the moist heat treated hollow fibers are then dried to remove moisture. Thereafter, stretching and heat treatment may be performed as necessary to fix the internal structure of the obtained polyamide hollow fiber membrane and further orient the crystal lamellae. This is usually less than 50% stretching or 16% stretching.
This is done by stress heat treatment at 0°C or lower.

The polyamide used in the present invention includes nylon 6,
Examples include common crystalline polyamides such as nylon 66, nylon 12, nylon 11-610, and nylon 46. Further, the polyamide may contain various additives, such as a nucleating agent, a matting agent, a pigment, a dye, an antioxidant, and an ultraviolet absorber, as necessary.

The present invention will be further explained below with reference to Examples.

Example 1 Nylon 6 chip (polymer concentration 1%, 98% sulfuric acid solvent,
The relative viscosity of sulfuric acid measured at 25°C is 3.55) and 290
At spinning temperature of °C, outer diameter/inner diameter 10゜0mm/9.4m
Discharge amount 3 g-m using a core-sheath type hollow fiber nozzle
At the same time, 9 ml/m of heat medium silicone (Toshi Silicone S H211) was discharged into the hollow part.
The yarn spun by injecting at a discharge rate of 1-.5
After cooling with cold air of ml・sec', 40m-m1
I wound it up with Row 1. The density of this hollow fiber is 1.122g
-cm'''3, and the birefringence was 0.7X10-3.

This hollow fiber was stretched 2.0 times to have a density of 1.125g-
cm-3 and birefringence of 23.2×1,00″3, the sample was kept under no tension and immersed in an aqueous solution containing 1% potassium iodide, and then set in an autoclave.

The treatment was terminated when 4.5 kg-clTl-2 of saturated steam was introduced into the autoclave and treated for 10 minutes, and the treated hollow fibers were taken out, washed with water, and then dried. The density of this moist heat-treated hollow fiber is 1.160 g-cm-3, and the birefringence is 3.
0.5X1.0-3, and the elastic recovery rate E at 50% elongation
R50 was 81%. In addition, the nitrogen permeability at 50% elongation is 9. 4X10-5cm-3・cm-2・s
The measurement result was ec-2/cmllg-1. Furthermore, when this moist heat treated hollow fiber was observed under an electron microscope, a fine porous structure was observed.

Comparative Example 1 In Example 1, the saturated water vapor pressure was set to 5. When moist heat treatment was carried out under the same conditions and method except that the weight was increased to 6 kg-cm-2, the hollow fibers after the treatment melted into a lump.

Comparative Example 2 The undrawn hollow fiber obtained in Example 1- was subjected to moist heat treatment under the same conditions as Example 1, but the density of the moist heat treated hollow fiber was i,
l-32g-cm', birefringence is 3.5X]-0-3
, the elastic recovery rate ER50 at 50% elongation is 57%, 5
The nitrogen permeability at 0% elongation is OC “3 cm-211
sec -2φcml1g'.

Comparative Example 3 When wet heat treatment was carried out under the same conditions and method as in Example 1, except that knots were made at both ends of the hollow fibers, cracks were observed in the hollow fibers after the treatment. Only leak threads were obtained.

[Effects of the Invention] According to the present invention, a polyamide hollow fiber membrane having an internal structure exhibiting excellent elastic recovery properties and microporous formation properties can be obtained, and the polyamide hollow fiber membrane can be easily produced.

Claims (2)

[Claims] (1) Birefringence in the orientation direction is 25×10^-^3~40×
10^-^3, density is 1.150 g cm^-^3 or more, elastic recovery rate at 50% elongation is 70% or more, and nitrogen permeability is 1.0 x 10^-^ at 50% elongation. 5cm＾-
＾3・cm＾-＾2・sec＾-＾2・cmHg＾-＾
1 or more polyamide hollow fiber membranes. (2) Birefringence is 15×10^-^3 to 35×10^-^
3. A method for producing a polyamide hollow fiber membrane, which comprises opening both ends or one end of the polyamide hollow fibers and subjecting them to a moist heat treatment using pressurized saturated steam or pressurized hot water while keeping them in a tension-free state.