JPH06228809A - High strength polyethylene fiber - Google Patents

Abstract

PURPOSE:To provide the high strength porous fiber comprising polyethylene having a less weight than those of other polymer raw materials, excellent in adhesivity to matrix materials, and having a low cost. CONSTITUTION:The high strength polyethylene fiber having a fiber diameter of 1-500mum and a tensile strength of >=8g/cm<3> is characterized in that the fiber comprises polyethylene having a density of >=0.960g/cm<3>, preferably >=0.965g/cm<3>, and a mol.wt. of 150000-1000000, preferably 200000-1000000, that the center of the fiber is substantially non-porous, and that fine pores having an average pore diameter of 0.01-2mum exist in a porosity of 20-90% in a range of 0.2-5mum in thickness from the surface of the fiber.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a new reinforcing high-strength polyethylene fiber suitable for use in fields requiring mechanical strength such as resin reinforcement and cement reinforcement.

[0002]

2. Description of the Related Art The following method is known as a method for producing a polyethylene high-strength fiber. The first is a gel stretching method, specifically, a polymer bullet.
in, Vol. 1, page 133 (1979). Since this method uses a solvent, there is a problem that the cost is high and the solvent remains.

The second method is the die drawing method, which is disclosed in British Patent No. 2060469. Although this method has a characteristic of not using a solvent, it has a fatal defect that its adhesion to a matrix material is poor when it is used as a reinforcing material because it is non-porous.

[0004]

An important property required of high-strength fibers as a reinforcing material is adhesiveness with a matrix material. Fibers with insufficient adhesive strength do not exhibit sufficient strength. Conventional materials have a problem in this respect, and surface treatment such as plasma etching treatment is performed to improve adhesiveness, which is a factor of high cost.

Polyethylene is widely used as a strength material because it has a great feature that it is lighter than other polymer materials. However, it is a low-cost fiber material that is lighter in weight and excellent in adhesiveness with a matrix material. Is desired. In order to solve such a problem, the present inventors have earnestly studied to obtain a high-strength porous fiber made of polyethylene which is lightweight and has excellent adhesiveness, and has arrived at the present invention.

[0006]

The gist of the present invention is that the central portion is substantially non-porous, and 0.2 to 5 .mu.m from the fiber surface.
In the region of m, fine pores having an average pore diameter of 0.01 to 2 μm are present with a porosity of 20 to 90%.
It is a high-strength polyethylene fiber of 500 μm and a tensile strength of 8 g / d or more.

The present invention will be described in more detail below. The polyethylene used in the present invention is preferably high-density polyethylene with few branches, and has a density of 0.960 g / cm.
^{It is 3} or more, preferably 0.965 g / cm ³ or more.

The molecular weight of polyethylene used in the present invention is 1
The range is 50,000 to 1,000,000, and more preferably 200,000 to
It is in the range of 1 million. When polyethylene having a molecular weight of less than 150,000 is used, the tensile strength of the present invention is 8 g / d.
The above porous fibers cannot be obtained. Further, it is difficult to form fine pores on the fiber surface with polyethylene having a molecular weight exceeding 1,000,000.

In the fiber of the present invention, micropores are opened from the surface of the fiber to the central portion in a region of 0.2 to 5 μm, preferably 0.2 to 2 μm. Since such fine pores are formed on the fiber surface, they firmly adhere to the matrix by the anchor effect.

Adhesive strength with the matrix is insufficient only by opening pores in a region of less than 0.2 μm from the fiber surface.
When the pores are opened up to a region exceeding 5 μm, the strength development of the fiber becomes insufficient.

Considering the balance between the strength development of the fiber and the adhesive force, the non-porous portion in the central portion has a non-porous portion / fiber radius of 60 to 99.92%, more preferably 65 to 9%.
0% most preferably 70 to 80%, and the remaining surface area is an area where micropores are formed.

The average pore size of the fine pores is 0.01 to 2 μm. If the pores are less than 0.01 μm, the adhesion to the matrix will be poor. If the pores are more than 2 μm, the strength development of the fiber is insufficient.

The porosity of the fine holes is 20 to 90%. It is more preferably 25 to 80%. If the porosity is less than 20%, the adhesion to the matrix is poor and the effect of weight reduction is small. If the porosity exceeds 90%, strength development is insufficient.

The shape of the micropores is not limited, but slit-shaped micropores extending in the fiber axis direction are particularly preferable from the viewpoint of adhesiveness to the matrix.

The diameter of the fibers is 1 to 500 μm. It is more preferably 3 to 200 μm, still more preferably 5 to
It is 100 μm.

The strength of the fiber is 8 g / d or more, preferably 10 g / d or more.

The fiber of the present invention may be produced by any method, but the melt shaping / drawing method is particularly excellent as a method for obtaining a high-strength surface porous fiber at low cost. Hereinafter, one method for producing the fiber of the present invention will be described.

In order to stably obtain the fiber of the present invention, it is desirable to set the spinning temperature to a temperature in the range of 40 to 150 ° C. higher than the melting point of the polymer. When spinning is carried out in a temperature range lower than this temperature range, the polymer is incompletely melted and melt fracture tends to occur, resulting in a decrease in stability in the drawing step. On the contrary, when spinning is performed in a temperature range higher than this temperature range, it becomes difficult to make it porous.

The polymer discharged at the appropriate spinning temperature is
It is desirable to pick up in the range of spinning draft 5 to 6000. If the spinning draft exceeds 6000, unstretched fibers capable of total stretching of 400% or more cannot be obtained. If the spinning draft is less than 5, highly oriented unstretched fibers cannot be obtained, and stretching porous cannot be performed.

The unstretched fiber thus obtained is an unstretched fiber in which lamella crystals are highly oriented and laminated in the fiber axis direction.
This unstretched fiber has a temperature of 100 to 130 ° C., more preferably 1
It heat-processes on temperature conditions of 15-130 degreeC, and is used for extending | stretching. The necessary heat treatment (annealing) time is 1 minute or more and 1 hour or less.

An annealing rate of less than 1 minute cannot achieve a porosity of 20% or more. Annealing for more than 1 hour is not preferable because it will open up to the center of the fiber during drawing.

Then, the film is stretched at about room temperature by about 10 to 100%. Then, in the temperature range of 90 to 130 ° C., thermal stretching is performed so that the deformation rate is 10% or more per second and the total stretching amount is 10 times or more, and the fiber surface is made porous. Thus, a high-strength fiber having a heterogeneous structure in which the fiber surface has pores having a fiber strength of 8 g / d or more can be obtained. The shape of the fiber may be circular, elliptical, triangular, or any other irregular shape.

[0023]

The present invention will be described in detail with reference to the following examples. Example 1 High-density polyethylene having a density of 0.960 g / cm ³ and a molecular weight of 220,000 was extruded from a nozzle at a spinning temperature of 232 ° C. and a fiber having a draft ratio of 185 and a diameter of 38 μm was wound.

This unstretched fiber was annealed at 125 ° C. for 2 minutes, then stretched 70% at room temperature and then at 125 ° C.
Stretching was carried out in a heating oven heated at 1% at a deformation rate of 12% per second until the total stretching amount became 13 times, to produce a fiber having a continuously porous surface.

The fiber thus obtained had a diameter of 26 μm, fine pores having an average pore diameter of 0.31 μm and a fine pore having a thickness of 1.8 μm from the fiber surface were opened with a porosity of 65%, and the central portion was substantially non-porous. It was porous. The tensile strength was 14 g / d.

Example 2 A high-density polyethylene having a density of 0.960 g / cm ³ and a molecular weight of 280,000 was extruded from a nozzle at a spinning temperature of 240 ° C. and a fiber having a draft ratio of 92 and a diameter of 75 μm was wound.

The unstretched fibers were annealed at 120 ° C. for 5 minutes, stretched 50% at room temperature and then heated in a heating oven heated to 125 ° C. at a deformation rate of 15% per second to give a total stretch of 16 times. Was continuously stretched to produce a fiber having a continuously porous surface.

The obtained fiber has a diameter of 61 μm, and an average pore diameter of 0.15 μm at a thickness of 1.2 μm from the fiber surface.
Micropores were open with a porosity of 59%, and the central part was substantially non-porous. The tensile strength was 17 g / d.

[0029]

The high-strength polyethylene fiber of the present invention has a porous structure on the fiber surface side and a non-porous structure on the center side. Therefore, it is lightweight and has excellent adhesiveness to the matrix. It is extremely excellent.

Claims (1)

[Claims] 1. A center part is substantially non-porous, and an average pore diameter of 0.01 to 5 μm in a region of 0.2 to 5 μm from the fiber surface.
Fiber diameter 1 to 500 μm, tensile strength 8 g / d, characterized in that 2 μm micropores are present with a porosity of 20 to 90%
High strength polyethylene fiber.