JPH04146208A - Porous polyethylene fiber and its production - Google Patents

Abstract

PURPOSE:To obtain the subject fiber having high porosity and excellent heat- insulation and useful for clothes, etc., by melt-spinning a high-density PE having a melt index falling within a specific range and subjecting the obtained fiber to specific annealing treatment and drawing treatment. CONSTITUTION:The objective fiber having an average microfibril length of 3-15mum, an average micropore diameter of 2-10mum and a porosity of 75-95% can be produced by melt-spinning a high-density PE having a melt index of 0.05-6.0, annealing the fiber at 100-130 deg.C for >=30min, cold-drawing at a draw ratio of 5-150% and subsequently hot-drawing at 100-l30 deg.C at a drawing rate of <=10%/sec and a total draw ratio of 750-2,000%.

Description

[Detailed Description of the Invention] [Industrial Field of Application] The present invention is applicable to the field of clothing such as synthetic cotton, nonwoven fabrics, and woven fabrics.
The present invention relates to a porous polyethylene fiber having a large pore size and high porosity, which is extremely lightweight and has excellent heat retention properties, and a method for producing the same.

[Prior art and problems to be solved by the invention] Japanese Patent Application Laid-open No. 1973
Publication No. 7-66114 describes porous polyethylene hollow fibers, but there is only description of 4 in which the average pore diameter of micropores measured with a mercury porosimeter is 2 μm or less, and one with large pore diameters has not been obtained. Also, U.S. Patent No. 4549.7
As disclosed in the specification of No. 45, for polypropylene, it is possible to relatively stably spin an undrawn yarn with a small fiber diameter that can be made porous, but it is only possible to obtain a yarn with smaller micropores than polyethylene. Moreover, as the stretching ratio is set lower, the rearrangement of the molecular chains progresses, causing the collapse of micropores, and the porosity actually decreases. It is difficult to obtain porous fibers.

The present invention solves these conventional problems and provides a porous polyethylene fiber with a large pore diameter and high porosity, and a method for producing the same.

[Means for solving problems]

That is, the gist of the invention is that it is made of high-density polyethylene with a melt index value (MI value) of 0.05 to &0, and is surrounded by nodules consisting of microfibrils arranged in the length direction of the lt&long fibers and stacked lamellae. The microfibrils have an average length of 3 μm to 15 μm, and the average pore diameter of the micropores measured with a mercury porosimeter is is 2 am to 10 μm, porosity is 75%
Porous polyethylene fiber characterized by having a value of ~95 and a melt index value (MI value) of [105~&
Melt-spun high-density polyethylene with a temperature of 100°C to
After annealing for 30 minutes or more at a temperature of 130°C,
5%~1sO4 cold stretching and stretching [t, n at 100℃~13
When hot-stretching at a temperature of 0°C, the deformation rate during hot-stretching is 10 widths per second or less, and the total stretching ratio is 750% to 200%.
The above method for producing porous polyethylene fibers is characterized in that the porous polyethylene fibers are porous.

The present invention will be explained in detail below.

The polyethylene used in the present invention needs to have high density with few branches,
The density according to the measurement method shown by 051C is at least (1960 t/ex" or more, preferably α965 t/ex")
cps" or more. By melt-shaping this polyethylene under specific conditions and further stretching it under specific conditions, fibers with aggregated micropores can be obtained.

The MX value uα of the polyethylene used in the present invention is in the range of 05 to &0.

The MI value is a value measured by M8'rM f)-1238, and is preferably in the range of a1 to i5. M
When using polyethylene with an I value exceeding &0, 7
It is impossible to draw to a total draw ratio of 504 or more, and the high porosity fiber of the present invention cannot be obtained. Also, M.I.
Polyethylene having a value of less than 1L05 has too high a melt viscosity, making stable spinning difficult. One of the important points of the present invention is to use high molecular weight polyethylene within a range that allows stable spinning.

The denyl per single fiber of the porous fiber of the present invention may be about the same as that of ordinary filaments that have been conventionally widely used for clothing, and from the viewpoint of processability into textile fabrics etc.
Preferably it is 20 cl/f.

In order to stably obtain the porous fiber of the present invention, the spinning temperature is desirably set within a range of 20°C to 100°C higher than the melting point of the polymer.

If spinning is performed at a temperature lower than this temperature range, the polymer will be incompletely melted and melt hook char will likely occur, resulting in decreased stability during the stretching process. Conversely, when spinning is performed in a temperature range below this temperature range, it is difficult to increase the porosity.

It is desirable that the polymer discharged at a suitable surface spinning temperature be withdrawn at a spinning draft in the range of 5 to 6,000. If the spinning draft exceeds 6,000, an undrawn yarn that can be drawn to a total of 7,504 or more cannot be obtained. If the spinning draft is less than 5, highly oriented undrawn yarn cannot be obtained and it is impossible to make the yarn porous by drawing.

A spinning nozzle with a circular cross section is usually used when producing undrawn yarn, but it is also possible to use a spinning nozzle with an irregular cross section such as an X-shaped cross section, an X-shaped cross section, or a rectangular cross section. When processed into knitted fabrics or nonwoven fabrics, the irregular cross-section fibers have improved bulkiness and a very soft texture compared to circular cross-section yarns having the same denier and porosity. In addition, when fibers are laid out in a tow shape and gas is flowed in the longitudinal direction of the fibers, as in a cigarette filter, circular cross-section yarns tend to have a high packing density, which increases ventilation resistance.

Therefore, when used in such applications, it is possible to create a filter that has low current carrying resistance, is less likely to cause drift, and has good filtration efficiency by using yarn with an irregular cross section that has good bulk. .

The undrawn yarn obtained by sniffing is highly oriented in the fiber axis direction. This undrawn yarn is heat-treated at a temperature below the melting point of the polymer, preferably below 130°C and above 100°C, and then subjected to drawing, if necessary. More preferable conditions are 115
℃ or higher. The required annealing time is 30 minutes or more.

This annealing makes the crystal structure more perfect,
An elastic recovery rate u504 or higher upon elongation is achieved.

It is desirable that the stretching be carried out in two stages, in which cold stretching is followed by hot stretching. In order to destroy the #'i crystal structure and uniformly generate microcrazes during cold drawing, it is preferable to fix the drawing point, and it is also desirable to carry out the cold drawing at a high drawing speed of 40 mm or more per second. Furthermore, in order to relax or break the crystal structure and generate microcrazes, the stretching temperature is preferably 40° C. or lower.

In this way, cold stretching is performed by approximately 5% to 1504%! After carrying out the stretching for i times, hot stretching is carried out in a temperature range of about 100°C to 130°C. If the hot stretching temperature exceeds 130°C, *a becomes transparent and it is difficult to obtain a desired porous structure.
If the temperature is below 00°C, the porous structure becomes fine and the porosity decreases, making it difficult to put it into practical use. It is an extremely important requirement of the present invention that the deformation rate #i1e during hot stretching be 10 or less. For deformation speeds above 104, 75
It is virtually impossible to obtain a total stretching ratio of 0.04 or more. The total stretching ratio must be 750% to 2Q (104%).

Stretching exceeding 2[1004 mL is undesirable because thread breakage occurs frequently during rt stretching and process stability decreases. 7504
Although a porous structure is formed at a stretching ratio of less than 1, the polyethylene fibers of the present invention having large pore diameters and high porosity cannot be obtained. In order to achieve a porosity of 754 or more using the stretch pore opening method, a total draw ratio of 7504 or more is essential.

The thus obtained polyethylene fiber with a large pore diameter and high porosity has characteristic strip-shaped micropores arranged in the fiber length direction and surrounded by nine microfibrils and nodules consisting of stacked lamellae. and the average length of microfibrils is 3uW@~15μm.

The large pore diameter and high porosity polyethylene fiber of the present invention is
It is an extremely clean material because it is manufactured using melting and heat forming methods that do not use any solvents.

〔Example〕

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

Example 1 High-density polyethylene with a density α968 iF/cm” and a melt index [1,7] was used with a nozzle diameter toms.
Using a 40-hole nozzle, a slow cooling section with a length of 5 mm and an atmosphere of 1 degree and 70 degrees Celsius was provided directly below the nozzle, and the spinning temperature was 180 degrees.
°C, spinning draft 102, winding speed 100 m/mi
It was spun and wound under conditions of n.

This undrawn yarn was heat treated at 125° C. for 24 hours at a constant length. The elastic recovery rate of this undrawn hollow fiber was 724. Subsequently, after stretching 1104 times at a stretching speed of 160 tatami per second at room temperature, the total amount of stretching was 1 on a heated surface heated to 118°C.
The porous polyethylene fiber was continuously produced by stretching in a roller at a deformation rate of 4.54 per second until the fiber became 3004. The obtained porous polyethylene fiber was drawn 14.0 times as much as the undrawn yarn, and was &5 d/f. The porosity measured with a mercury porosimeter was 844, and the average pore diameter was 2.5 μm.

When observed with a scanning electron microscope, there were numerous characteristic short-rib-like small holes, and the average length of the fibrils was 7.0 mm.
It was pIll.

Example 2 High-density polyethylene with a density of 1968 t/ex'' and a melt index of S5 was spun using a nozzle with a nozzle diameter of 10-140 holes, at a spinning temperature of 165°C and a spinning draft of 204.
The fibers were spun and wound at a winding speed of 200 spins/min.

This undrawn yarn was heat treated at 120° C. for 24 hours at a constant length.

The elastic recovery rate of this undrawn yarn was 73. Subsequently, after stretching 80 widths at room temperature at a stretching ratio of 1,604 per second, the deformation rate was kept at a deformation rate of '!' per second until the total amount of stretching reached 8,004 in a heating box heated to 125°C. -04IC was drawn between rollers, and heat setting was performed for 40 seconds in a heating box heated to 125°C to continuously produce porous polyethylene fibers.

The obtained porous polyethylene fiber in has been drawn 90 times as much as the undrawn yarn, and has an X? It was d/f.

The porosity was F182% as measured by a mercury boron meter, and the average pore diameter was 2.1 μm. When observed with a scanning electron microscope, numerous characteristic small holes were present, and the average length of the fibrils was 58 μm.

Comparative Example 1 Density 1968 f/ex”, melt index and 7
Spinning was performed under the same conditions as in Example 1 using high-density polyethylene.

This undrawn yarn was heat-treated and drawn under the same conditions as in Example 2, but yarn breakage occurred frequently during hot drawing, and uniform drawing with a total draw ratio of 750 was impossible.

〔Effect of the invention〕

Polyethylene track of the present invention! L is a fiber with a large pore diameter and high porosity, in which strip-shaped micropores formed by being surrounded by microfibrils and nodules consisting of stacked lamellae are connected throughout from the fiber surface to the center. can be,
It is lightweight and has excellent heat retention properties, and can be applied to the field of clothing such as synthetic cotton, nonwoven fabrics, and woven fabrics, and its industrial value is extremely large.

Patent applicant: Mitsubishi Rayon Co., Ltd.

Claims (2)

[Claims] (1) Melt index value (MI value) is 0.05 to 6
．． The fiber is made of high-density polyethylene, and the strip-shaped micropores, which are formed by being surrounded by microfibrils arranged in the fiber length direction and nodules made of stacked lamellae, communicate throughout the fiber from the surface to the center. It is a thing,
The average length of the microfibrils is 3 μm to 15 μm,
The average pore diameter of micropores measured with a mercury porosimeter is 2.
A porous polyethylene fiber having a diameter of μm to 10 μm and a porosity of 75% to 95%. (2) Melt index value (MI value) is 0.05 to 6
．． Melt-spun high-density polyethylene at 100°C
After annealing at a temperature of ~130°C for 30 minutes or more, cold stretching is performed by 5% to 150%, followed by 100°C to 130°C.
When hot-stretching at a temperature of
The method for producing porous polyethylene fibers according to claim 1, characterized in that: