JP2002137276A - Method for manufacturing profile porous body made of ultrahigh molecular weight polyethylene - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method capable of continuously obtaining a profile porous body made of ultrahigh mol.wt. polyethylene having a complicated cross- sectional shape by extrusion molding. SOLUTION: Ultrahigh mol.wt. polyethylene melted at 150-300 deg.C is extruded from linear slits 15 and molten state parts are mutually welded in a mold having a profile cross section connected to the linear slits 15 and the molded porous body having a large number of open voids and having a profile cross-sectional shape is sintered.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing an irregularly shaped porous body made of ultra-high molecular weight polyethylene, and more particularly to a method for producing a gas or liquid having a large number of continuous pores, excellent permeability and chemical resistance. Filtration filters for separating fine dust, particles, and other substances from the medium, carriers of specific participants in the reaction or treatment process, air diffusers in aeration tanks, ultra-high water used in permeation pipes and drain pipes of groundwater, etc. The present invention relates to a method for producing a modified porous body made of high molecular weight polyethylene.

[0002]

2. Description of the Related Art Conventionally, as a filter or the like, a cylindrical porous body formed by sintering ultra-high molecular weight polyethylene into a pipe shape or a rectangular porous body having corrugated folds on its outer surface. It has been known. In particular, a porous body having a pleated portion formed on a cylindrical body wall and having a modified cross section has an advantage that the filtration area is large and the filtration ability is excellent (see JP-A-9-313834). ).

[0003]

However, a conventional porous body having an irregular shape is characterized in that an ultra-high molecular weight material serving as a raw material is provided in a gap between a cylindrical inner die forming an inner surface and a cylindrical outer die forming an outer surface. It has been manufactured by a method of filling polyethylene particles and heating and sintering the particles, that is, a so-called sintering method. For this reason, the length of the porous body to be manufactured is limited, and
Because of the batch system, there was a limit to the improvement in manufacturing efficiency. In addition, continuous production of a porous body by extrusion molding is also performed. In this case, a cylindrical body having a simple sectional shape is mainly used, and a porous body having a complicated irregular sectional shape such as a star is used. It was difficult to obtain a body.

[0004] Therefore, an object of the present invention is to provide a method capable of continuously obtaining a modified porous body made of ultra-high molecular weight polyethylene having a complicated cross-sectional shape by extrusion molding.

[0005]

Means for Solving the Problems To achieve the above object, a method for producing a modified porous body made of ultra-high molecular weight polyethylene according to the present invention comprises: extruding ultra-high molecular weight polyethylene with an extruder; A method for producing a deformed porous body, comprising extruding ultra-high molecular weight polyethylene in a molten state at a heating temperature of 150 to 300 ° C. from a linear slit having a deformed cross section provided at the extruder tip, By fusing the molten portions to each other in a molding die having an irregular cross-section connected to the linear slit, extrusion molding is performed while sintering a porous body having an irregular cross-section having a large number of continuous pores. Features.

[0006]

FIG. 1 is a cross-sectional view showing a main part of an extruder to which a method for producing a modified porous body made of ultrahigh molecular weight polyethylene according to the present invention is applied, and FIG. 2 is an explanatory view showing a shape change during molding. It is.

According to the method of the present invention, an ultrahigh molecular weight polyethylene as a raw material is extruded from an extruder to form a die 11 and a molding die 1.
2 is continuously formed to continuously form an ultra-high molecular weight polyethylene irregularly shaped porous body having a predetermined shape.

The ultra-high molecular weight polyethylene in the molten state, which is melted and pressurized in the extruder, is extruded from the die 11 into the relatively low-pressure molding die 12 at once to be in a state of discrete particles. It becomes a flow state.

The ultra-high-molecular-weight polyethylene, which is in a molten state in a particle state by the flash flow, generates an internal pressure due to the resistance of the inner surface of the molding die 12 at a relatively low temperature, and the particles are welded to each other by the internal pressure. A gap (hole) is formed to form a porous body.

As the extruder, a single-screw extruder or a twin-screw extruder having a large extrusion amount can be used. Among various extruders, the co-rotating twin-screw extruder is extremely effective in kneading, so that the particles during flash flow become extremely small, and the particles are compressed even by a low pressure in a molding die thereafter. Porosity tends to be insufficient.

On the other hand, the twin screw extruder of the opposite direction is difficult to apply a shearing force to the melted ultra-high molecular weight polyethylene, and it is difficult for the kneading to be effective. It has the advantage that the control of the hole diameter in the mold is easy, and among them, the counter-rotating twin-screw conical extruder has the advantage that the throughput is large.

The ultra high molecular weight polyethylene used as the raw material has a molecular weight of about 1 to 5,000,000 and a melting point of 135 to 140.
° C, the bulk density is 0.35 to 0.45 g / cm ³ , the melt flow rate (MFR) is 1.0 or less, particularly 0.1 or less,
It is more preferably 0.01 or less, and the extruder is charged in a state of particles having an average particle size of about 5 to 1000 μm.

Ultra-high molecular weight polyethylene is excellent in wear resistance, self-lubricating property, impact resistance, chemical resistance and the like, and is suitable for a wide variety of uses as a material of a deformed porous body. Also, compared to other thermoplastic resins, ultrahigh molecular weight polyethylene has the advantage that flash flow from linear slits is more likely to occur within the range of normal extrusion conditions. Other thermoplastic resins such as low molecular weight polyethylene hardly have a flow behavior such as a flash flow even when extruded from a linear slit, and hardly form a particle state.

Further, a powder of a crosslinked polyolefin resin containing, for example, a fluororesin or a low-density polyethylene by irradiation with radiation is added to the ultrahigh molecular weight polyethylene in an amount of 1 to 50.
A material added in an amount of about mass% can be used as a raw material, and in addition, carbon black or the like can be added.

A die 11 and a molding die 12 for molding the above ultrahigh molecular weight polyethylene composition (hereinafter, sometimes referred to as a raw material resin) into a deformed shape, for example, a star shape, include:
After forming a basic shape of a star cross section by the die 11, a predetermined star cross section is formed by the molding die 12. That is, in the die 11, as shown in FIG. 2, the raw resin P is sent out from the ring-shaped mouth 13 to the star forming part 14 in the first block as a cylindrical shape as shown in FIG. As shown in FIGS. 2 (B) to 2 (I), the star forming portion 14 is formed with a concave portion Q by gradually narrowing the raw material resin P from the outside, thereby forming a predetermined star-shaped basic shape. It is extruded from a linear slit 15 having a star-shaped cross section at the tip of the die 11 and having an interval smaller than the thickness of the star-shaped porous body to be manufactured. It is fed in a molten state into a molding die 12 having a corresponding interval.

The linear slits 15 are 150 to 300
℃, the raw material resin in a molten state
2 to be extruded. At this time, the interval between the linear slits 15 and the heating temperature are appropriately set depending on the properties of the raw material resin and the shape, size, thickness, extrusion speed, and the like of the irregularly shaped porous body to be produced. It is preferable that the temperature is about 5 to 30% of the thickness of the product and the temperature is higher than the melting point of the raw material resin and about 50 to 100 ° C. higher than the melting point.

If the distance between the linear slits 15 is too large, flash flow is difficult to occur, and if it is too small, extrusion becomes difficult. If the temperature is too low, the raw resin can be melted. If the temperature is too high, there is a problem that deterioration such as thermal decomposition is apt to occur.

The raw material resin which has entered the molding die 12 in a molten state from the linear slit 15 is heated at a temperature lower than the linear slit 15, for example, at a temperature lower by about 40 to 80 ° C. than the slit 15. The molten portions are gradually welded to each other while being gradually cooled by the mold 12, and sintering is completed in the molding die 12 to form a predetermined star-shaped porous body. The star-shaped porous body coming out of the molding die 12 is cooled and cut into a predetermined length in the same manner as in a usual extrusion molding method.

At this time, if the temperature of the molding die 12 is lower than the temperature of the linear slit 15 by 150 ° C. or more, the friction with the ultrahigh molecular weight polyethylene becomes too large, and the particles tend to adhere to each other. It is hard to be in a state. If the temperature is equal to or higher than the temperature of the linear slit 15, the friction with the ultra-high molecular weight polyethylene particles is reduced, and a pressure sufficient for welding the particles is not generated. Also, the molding die 12
The length varies depending on the temperature condition, the thickness condition of the porous body, and the like, but it is sufficient that the molded body (irregular porous body) coming out of the molding die 12 can maintain a predetermined shape.
Usually, it is about 5 to 10 cm.

The size of the irregularly shaped porous body that can be produced depends on the capacity of the extruder, but generally, the maximum dimension on the outer surface side is 4 mm.
mm or more, the inner side minimum dimension is about 2 mm or more,
The thickness is about 1 mm. Further, the number of irregularly shaped irregularities is arbitrary, but usually six or more are preferable.

As described above, the ultra-high molecular weight polyethylene in a molten state is extruded from the linear slits 15 having a smaller interval than the thickness of the irregularly shaped porous body to be a product into the molding die 12 having a predetermined shape. Welding the molten state parts to each other while slightly expanding the inside, maintaining the bent part, which is difficult to maintain the shape by ordinary extrusion molding method, in a predetermined shape, while maintaining a porous shape with a large number of continuous pores The body can be sintered.

In the die 11 in the above embodiment,
First, a large cylindrical cross section is formed and then squeezed sequentially from the outside. However, as shown in a die 21 shown in FIG. It is also possible to use one that forms a star-shaped basic shape at the linear slit 23 at the tip while expanding to
A die having any structure can be appropriately selected according to the size of the deformed porous body. At this time, the same mold as that of the above-described embodiment can be used for the molding die 24 connected to the die 21.

[0023]

As described above, according to the method for producing a modified porous body made of ultra-high molecular weight polyethylene according to the present invention, the modified basic shaped body extruded in the molten state from the linear slit of the extruder is formed into a linear form. Since the molten parts are sintered together in the molding die connected to the slit while they are welded to each other, it is possible to continuously manufacture porous bodies with complex shapes such as complex stars by extrusion. In addition, the production efficiency of the irregular porous body made of ultrahigh molecular weight polyethylene can be greatly improved.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing a main part of an extruder to which a method for producing a modified porous body made of ultrahigh molecular weight polyethylene according to the present invention is applied.

FIG. 2 is an explanatory diagram showing a shape change during molding.

FIG. 3 is a cross-sectional view showing another example of the shape of a die.

[Description of Signs] 11: die, 12: molding die, 13: ring-shaped mouth, 1
4 ... star forming part, 15 ... linear slit, 21 ... die, 2
2 ... star forming part, 23 ... linear slit, 24 ... molding die, P ... raw material resin

Claims (1)

[Claims] 1. A method for producing a modified porous body made of ultra-high molecular weight polyethylene by extruding ultra-high molecular weight polyethylene with an extruder, comprising the steps of: By extruding ultra-high molecular weight polyethylene in a molten state at a heating temperature of 150 to 300 ° C. and welding the molten state parts together in a molding die having an irregular cross-section connected to the linear slit, a large number is obtained. A method for producing an irregularly shaped ultra-high molecular weight polyethylene porous body, comprising extruding a porous body having an irregularly shaped cross section having continuous pores while sintering the porous body.