JPS63219613A - Heterogeneous poromeric hollow fiber and production thereof - Google Patents

Abstract

PURPOSE:To obtain the titled lightweight fiber outstanding in heat retentivity and strength, suitable for sloth sector such as woven and nonwoven fabrics and synthetic fiber wadding and construction material sector, etc., by melt spinning of a thermoplastic polymer into hollow fiber followed by drawing under specified conditions. CONSTITUTION:A thermoplastic polymer such as polyester or polyamide is subjected to melt spinning at a draft ratio <=3,000 using a nozzle for hollow fiber production to form into hollow fiber. Thence, this fiber is drawn at a draw ratio ranging from 1.1 to 50, in such a temperature atmosphere as to be lower than the melting point of said polymer by >=10 deg.C at a deformation rate >=8X10<2>%/min, thus obtaining the objective fiber made up of (1) a porous layer 1 containing numerous fine pores 2 with an average diameter within the fiber section D 0.01-50mu and ratio of the average length oriented in the fiber direction L to said diameter D: L/D=2-100 and (2) two dense non-porous layers 3 and 3' in the outer and inner circumferences of the fiber, respectively.

Description

Detailed Description of the Invention (Industrial Field of Application) The present invention is a non-uniform fabric made of synthetic cotton, non-woven fabric, woven fabric, etc., which has excellent heat retention properties and is lightweight and strong, which can be applied to the clothing field and the building material field. The present invention relates to a porous hollow fiber and a method for producing the same.

(Prior Art) Several methods have been proposed as means for making thermoplastic polymers porous. For example, JP-A-47-1
No. 4418 discloses a method of forming a porous fibrous material by mixing a polymer mixture with an inorganic substance such as silica or talc, melt-molding the mixture, and then stretching the mixture. This method requires additives in addition to the thermoplastic polymer, and since the additives tend to fall off from the fibrous material after molding, it cannot be said that the product is stable in terms of strength and heat retention.

Furthermore, methods for obtaining porous hollow fiber membranes using hard elastic properties are disclosed in JP-A-52-15627 and JP-A-57-84702. Because controlling the structure is an extremely important factor, the materials that can be made porous are limited to specific polymers such as tactical polypropylene and high-density polyethylene, so it is difficult to say that this technology is versatile.

Moreover, in this technique, the porous structure is uniformly distributed in the thickness direction of the fiber, and a non-uniform porous structure cannot be obtained.

Furthermore, there are methods to make the fibers porous through post-treatment, such as the Nil processing method for polyester (for example, alkali treatment), but such methods have the disadvantage that alkali-dissolved substances remain attached to the fibers, and Since the surface becomes porous starting from the surface, a non-porous layer cannot be formed on the surface. Furthermore, the technology is not versatile because the polymer materials that can be processed are limited.

(Problems to be solved by the invention) In other words, with the conventional methods described above, impurities may adhere to or remain on the obtained fibers, there may be restrictions on the type of polymer used as a raw material, or the surface of the fiber may There are problems in that even parts of the polymer are homogeneously porous, resulting in a lack of stability in terms of shape, strength, and heat retention, or inability to be applied to all types of polymers, resulting in poor versatility.

The present invention has been made in view of these points, and is a hollow fiber that is lighter than conventional hollow fibers, has excellent heat retention, and has a non-uniform microporous interior that is stable in terms of strength and shape. The purpose is to provide fibers and to develop methods for producing the same.

(Means for Solving the Problems) For this reason, the inventors of the present invention have conducted extensive studies to improve the drawbacks of the prior art, and as a result, have arrived at the present invention.

The presence of an air layer is important in order to improve heat retention, and hollow fibers are already known as heat retention materials, but the inventors have developed a hollow fiber that has even better heat retention than conventional materials. I found it. That is, the present invention has developed a heterogeneous microporous hollow fiber that has a specific fine pore structure inside the hollow fiber and a dense non-porous structure at the outer and inner periphery of the fiber. be.

The hollow fiber of the present invention is lightweight and has excellent heat retention properties as well as excellent mechanical strength. Furthermore, it is an extremely versatile technology that can be applied to any material as long as it is a thermoplastic polymer.

The present invention provides fibers with the above-mentioned excellent properties as "heterogeneous microporous hollow fibers made of a thermoplastic polymer and having micropores arranged in the fiber direction, and having an average diameter in the fiber cross section of 0.5". A porous layer formed of micropores with a ratio L/D of 01 μm to 50 μm and an average length in the fiber direction and D of 2 to 100, and two dense non-porous layers on the outer and inner periphery of the fibers. The fiber is produced by using a thermoplastic polymer with a draft ratio of 30.
After melt molding into a hollow fiber shape at a temperature of 0.00 or less, the temperature is 300 °C lower than the glass transition temperature of the polymer and 10 °C lower than the melting point.
In a temperature atmosphere below ℃ low temperature and with a deformation rate of 8×1
02%/min or more at a stretching ratio in the range of 1.1 to 50. These configurations are intended to solve the above problems.

The heterogeneous microporous hollow fiber of the present invention is extremely unique in its fine pore structure. That is, the fibers are arranged in the fiber direction with an average diameter of 0.01μIIl to 50μm within the fiber cross section,
It has a porous layer having many elongated micropores whose average length to average diameter ratio L/D is 2 to 100, and a dense non-porous layer on the outer and inner periphery of the fibers. . The thickness of the non-porous layer is preferably 5% or more and 70% or less of the fiber wall thickness. In the hollow fiber of the present invention, the hollow portion and the micropore portion form an air layer, resulting in good heat retention. If the average diameter of the micropores is less than 0.01 μm, the heat retention is insufficient;
If the thickness is more than μm, it is insufficient in terms of maintaining strength. If the thickness of the non-porous layer is 70% or more of the longest diameter of the fibers, the heat retention property will be poor.

The proportion occupied by micropores (porosity) is preferably in the range of 20% or more and 90% or less. Hollow percentage of hollow fiber is 5%
It is preferable that it is in the range of 95% or more. If the hollowness ratio is 95% or more, the mechanical strength of the hollow fibers decreases, causing them to collapse or break.

Further, if the hollowness ratio is 5% or less, the heat retention property is poor. It goes without saying that the fiber form is not limited to a circular cross section, but can be made into various cross-sections with different diameters as necessary. The thickness of the fibers is not particularly limited, and any size can be selected depending on the purpose.

As a polymer material for obtaining such a heterogeneous microporous hollow fiber, a thermoplastic polymer such as polyester, polyamide, polyolefin, polyacetal, polycarbonate, polyurethane, polyphenylene sulfide, polysulfone, etc. can be used. Can be used. Moreover, it is possible to use not only a single polymer but also a mixture of two or more components.

Such heterogeneous microporous hollow fibers can be obtained by forming hollow fibers by melt extrusion and then stretching the fibers under specific conditions. Important requirements are spinning at a spinning draft ratio of 3000 or less, preferably 2000 or less, and then spinning at a temperature 10°C lower than the melting point (Tm) of the polymer, preferably (Tm) or less.
m-50) "8X1 in a temperature atmosphere below C.
Deformation rate of 0”%/min or more, more preferably 10”
It is important to stretch at a deformation rate of %/min or higher. In particular, the effect of deformation rate is large, 8×102%/mi
The heterogeneous microporous hollow fiber of the present invention cannot be obtained at a deformation rate of n or less. The stretching ratio can be arbitrarily selected within the range of 1.1 to 50. The heterogeneous microporous structure of the present invention is achieved for the first time through this stretching, and if necessary, so-called heat setting may be performed by passing through an atmosphere at a temperature higher than the glass transition temperature of the polymer.

FIG. 1 is a cross-sectional model diagram of a heterogeneous microporous hollow fiber that is one embodiment of the present invention. 1 is a porous layer, and 2 is a micropore. A major feature of the micropores 2 is that they are arranged in the fiber direction and elongate. In the figure, the micropores 2 are independent from each other, but adjacent micropores 2.2 may penetrate through them. 3 and 3' are dense non-porous layers formed on the outer and inner layers of the hollow fiber cross section, sandwiching the porous layer. 4 is the hollow part of the hollow fiber.

(Example) Hereinafter, the present invention will be explained in more detail with reference to Examples.

Example 1 Polyethylene terephthalate (intrinsic viscosity [η] = 0.7
After drying the chips of 2) by a known method, they were melted at 285° C. using a hollow fiber manufacturing nozzle having a double tube structure to produce hollow fibers at a draft ratio of 250. The obtained fiber was stretched at a temperature of 30°C and a deformation rate of 5.5 x 10'%.
The film was continuously stretched under the conditions of /min until the stretching ratio reached 7.0 times. A phenomenon in which the fibers whitened due to the formation of micropores during stretching was observed. The porosity estimated from the change in the shape of the fibers after drawing was 47%. When micropores in the fibers were observed using a scanning electron microscope, the inner diameter of the fibers was 20 μm, the outer diameter was 30 μm, and the fiber cross section had an average diameter of 0.7 μm.
The thickness of the porous layer in which there are countless pores with an average length of 7.5 μm in the fiber direction and the outer non-porous layer is 0.9 μm (
(18% of the wall thickness), the thickness of the inner non-porous layer is 0.8 μm
Two non-porous layers (16% of wall thickness) were observed.

Comparative Example 1 A polyethylene terephthalate hollow fiber filament produced under the same conditions as Example 1 was stretched at a stretching temperature of 30°C and a deformation rate of 2.
．． It was continuously stretched under the conditions of OX 10"%/win until the stretching ratio became 7.0 times. No whitening phenomenon of the fibers was observed during stretching, and observation using a scanning electron microscope showed that there were no micropores at all. I was not able to admit.

Example 2 Chips of polybutylene terephthalate ([η) = 0.91) were dried by a known method, and then melted at 250°C using a hollow fiber manufacturing nozzle with a double tube structure and at a draft ratio of 330. A hollow fiber was produced. The obtained fiber was stretched at a deformation rate of 9.6 x 10'%/min at a temperature of 30°C.
The film was continuously stretched under the following conditions until the stretching ratio reached 6.0 times. The drawn yarn had an inner diameter of 17 μm and an outer diameter of 29 μm, and the porosity estimated from the change in the shape of the fibers before and after drawing was 38%. When the structure of micropores was observed using a scanning electron microscope, it was found that there was a porous layer with numerous micropores with an average diameter of 0.2 μm and an average length in the fiber direction of 4 μm in the fiber cross section, and a non-porous layer on the outer periphery. The thickness of the material is 1.2μm (20μm of wall thickness)
%), and the thickness of the inner non-porous layer is 1.1 μm (1.1 μm of wall thickness).
Two non-porous layers of 8%) were observed.

Example 3 Polyphenylene sulfide (Philips Pet
1 ro-Ieum Rydon GPO2) chip
After drying with hot air at 50° C. for 3 hours, hollow fibers were manufactured using a hollow fiber manufacturing nozzle having a double tube structure and melting at 290° C. at a draft ratio of 490. The obtained fiber was stretched at a deformation rate of 6.8 x 10'%/at a drawing temperature of 25°C.
The film was continuously stretched under the conditions of l1lin until the stretching ratio became 5.0 times. Inner diameter after stretching is 16μm, outer diameter is 28μm
m, the porosity estimated from the shape change before and after stretching is 40%.
Met. When the micropore structure was observed using a scanning electron microscope, it was found that there is a porous layer in which there are countless micropores with an average diameter of 0.15 μm and an average length in the fiber direction of 3.7 μm in the cross section of the fiber, and a non-porous layer on the outer peripheral side. The thickness of the porous layer is 1.3 μm (22% of the wall thickness), and the thickness of the inner non-porous layer is 1.1 μm (
Two non-porous layers (18% of the wall thickness) were observed.

(Effects of the Invention) As explained above in detail, the heterogeneous microporous hollow fiber according to the present invention has fine elongated pores having a specific diameter and a specific length arranged in the fiber direction in the cross section of the fiber. In addition to the existence of the hollow part, a large number of fibers are formed in a state where they are gathered together to surround a hollow part, and the outer peripheral part and the inner peripheral part of the fiber are formed as a dense non-porous layer. The existence of fine pores in an independent state reduces the weight of the fiber significantly and further increases the heat retention of the fiber itself.Furthermore, the presence of the non-porous layer on the outer and inner periphery of the fiber makes the fiber The shape of the material is stabilized and sufficient strength is maintained.

In addition, the method for producing a heterogeneous microporous hollow fiber according to the present invention can produce a heterogeneous microporous hollow fiber having the above structure using any thermoplastic raw material polymer, as long as the method is carried out under specified conditions. This is an extremely versatile and effective method that can reliably obtain microporous hollow fibers.

[Brief explanation of the drawing]

The figure is a cross-sectional view of a model of a heterogeneous microporous hollow fiber that is one embodiment of the present invention. Explanation of the main parts of the diagram 1 - Porous layer 2 - Fine pores 3 - (outer periphery side) non-porous layer 3' - (inner periphery side) non-porous layer 4 - hollow part

Claims (1)

[Scope of Claims] 1. A heterogeneous microporous hollow fiber made of a thermoplastic polymer and having micropores arranged in the fiber direction, the fiber having an average diameter D in the fiber cross section of 0.01 μm to 50 μm. a porous layer formed from a large number of micropores having a ratio L/D of the average length L in the direction and the average diameter D of 2 to 100;
A heterogeneous microporous hollow fiber comprising two dense non-porous layers on the outer periphery and the inner periphery of the fiber. 2. After melt-molding a thermoplastic polymer into a hollow fiber shape with a draft ratio of 3000 or less, in an atmosphere at a temperature 10°C lower than the melting point of the polymer and at a deformation rate of 8 x 10^2%/min or more. A method for producing a heterogeneous microporous hollow fiber, which comprises stretching at a stretching ratio of 1.1 to 50.