JPS6140175B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a continuous extrusion molding method for thick-walled ultra-high molecular weight polyethylene and a molding apparatus used therefor.

The molecular weight of ultra-high molecular weight polyethylene is said to be about 500,000 or more by the viscosity method, about 1.5 million or more by the light scattering method, and 2 to 100,000 by the viscosity method of ordinary high-density polyethylene.
10,000, which is extremely large compared to 60,000 to 300,000 by light scattering method.
Impact resistance, abrasion resistance, stress resistance, crack resistance,
It has excellent low-temperature resistance and is expected to be used in fields that require a high degree of mechanical strength.

However, on the other hand, the melt fluidity of the resin is extremely poor, and it is difficult to measure it using the ordinary melt index measurement method even when the plunger load is increased. It is no exaggeration to say so.

Various methods have been proposed for molding such ultra-high molecular weight polyethylene. For example, injection molding is described in JP-A-51-81861, and melt-extrusion is described in JP-A-51-90360. has been done. In particular, the latter relates to the same melt extrusion method as the present invention, and its gist is that when melt extruding resin powder using a screw extruder, the resin is heated in the extruder at a temperature at least 40°C lower than the resin melting point. After the powder is compressed, it is melt-extruded in a conventional manner. This low-temperature compression prevents the resin and screw from rotating together and becoming impossible to extrude. This method has the advantage that it can be implemented by improving the screw of a single-screw extruder, but although it can be applied to thin products with a thickness of 5 mm or less and about 1 mm, It has been found that it is completely ineffective for extrusion molding of thick materials up to ~50 mm.

Therefore, we conducted various studies on continuous extrusion molding methods and equipment for thick-walled pipes or plates using ultra-high molecular weight polyethylene with a molecular weight of 500,000 or more. By introducing the resin without degassing, which is different from other methods, they were able to prevent the resin from rotating together, allowing stable press-fitting into the die, and by making improvements to the shape of the die, they were able to achieve sufficient degassing.

The feature of the manufacturing method of the present invention is that the ultra-high molecular weight polyethylene powder raw material is immediately and rapidly heated to a temperature above its melting point, and the granules containing air are granulated at a pressure of 15 to 200 kg. /cm ² , is melted by being press-fitted into a mold under high pressure and high temperature at a temperature of 160 to 330℃, and is extruded from a molding nozzle at a low speed of 0.15 to 10 m/hr while degassing by narrowing the passage inside the die. . They also developed an apparatus that embodies this manufacturing method, leading to the completion of the present invention.

A feature of the manufacturing apparatus is that the apparatus is configured into five sections: a cylinder zone, a heating melting zone, a heat insulation zone, a cooling zone, and a pressure correction zone, the specific structure of which will be described in detail later.

The ultra-high molecular weight polyethylene used here is already commercially available, and powder particles with a particle size of 100 to 300 μm are available. Its average molecular weight reaches over 500,000 when determined by the viscosity method, and over 1.5 million when determined by the light scattering method. Therefore, its physical properties are different from ordinary polyethylene,
It has extremely high impact resistance and is a non-destructive material that cannot be measured by the isot impact value of ASTMD 256, and even at abrasion levels of 70 mg/min by the taper method of ASTMD 1175.
This value is approximately 1/3 that of nylon resin, which is 1000 times. Although it has such excellent physical strength, it has extremely poor moldability and cannot be molded at all using ordinary melt extrusion molding methods or extrusion molding machines.
This makes ultra-high molecular weight polyethylene below its melting point.
High viscosity even when heated and melted above 130-140℃, MI≒
This is because it is 0.

The melt molding method and apparatus of the present invention are unique in that they are made of a resin with MI≈0 and can be continuously molded into thick-walled products by extrusion molding.

Hereinafter, the method and apparatus of the present invention will be specifically explained with reference to the drawings.

FIG. 1 is a sectional view of the cylinder zone, and FIG. 2 is a longitudinal sectional view of the main part of the extruder.

The method for forming the thick-walled molded product of the present invention is a continuous extrusion method, in which ultra-high molecular weight polyethylene powder is suddenly heated to a high temperature above its melting point, and then extruded into granules by pressurizing it while still containing air. It is press-fitting into the machine. The specific device is a cylinder zone 1 shown in FIG. 1, in which raw powder is supplied from a hopper 2 into a cylinder 4 heated by a band heater 3. In this case, the groove width of the screw 5 is compressed by changing the groove depth by keeping the same pitch and making the screw shaft gradually thicker. In conventional extruders, the temperature during compression is usually 10°C above the melting point of the resin.
This is carried out at a temperature of ~20° C., but under this condition, the ultra-high molecular weight polyethylene, which is the raw material of the present invention, causes co-rotation and cannot be extruded. Therefore, extrusion at a lower temperature of 40°C lower than the melting point has been carried out, but in the present invention, the temperature was suddenly increased to a temperature far higher than the melting point, ignoring the drawbacks of air. To give an example, 270℃ in C ₁ and C ₂ in the cylinder zone
It is 260℃. As a result, only the outer layer of the resin remained in the form of granules containing air, which melted, making it possible to extrude the resin into an extruder in an extremely stable and highly compressed state without rotating with the screw.

The granulated resin in the cylinder zone 1 is press-fitted into the heating melting zone 7 of the extruder main body 6. In the case of producing thick-walled pipes, the cross-sectional structure of the extruder main body 6 is shown in FIG. 2, and consists of a heat-melting zone 7, a heat-insulating zone 8, a cooling zone 9, and a pressure-correcting zone 10. This is exactly the same in the case of plate manufacturing.

The heating melting zone 7 is equipped with heating heaters 11 outside thereof in six divisions D ₀ to D ₅ so as to provide a temperature gradient from high temperature to low temperature between 330° C. and 160° C., and a movement gap for the resin raw material. It has a die structure in which the pressure can be increased within the range of 15 to 200 Kg/cm ² by sequentially narrowing 12. Since the melting point of the resin is about 136°C, the temperature is much higher than normal extrusion conditions. If the temperature is below 160°C, it is difficult to melt the resin, the molding speed becomes extremely slow, and it is impossible to expel air bubbles, resulting in poor productivity. Also, conversely, 330
When the temperature reaches a temperature higher than 0.degree. C., depolymerization occurs, resulting in a decrease in molecular weight. The more desirable temperature range is 290-170℃
It is. If the pressure inside the die is less than 15 kg/cm ² , it is difficult to match the product dimensions to the specified dimensions of the die. The high pressure may be 200 kg/cm ² or more, but it is unnecessary and uneconomical because there is a problem with the pressure resistance of the device. Generally, a pressure of 40 to 80 Kg/cm ² is a more preferable range for operation.

D ₀ and D ₁ are preheating die parts, e.g. 250-290
The temperature is the same as or higher than that of the cylinder part, where it completely melts while reaching D ₂ , and after expelling air bubbles under high pressure, it is led to an even higher compression zone of D ₄ to _{D 5} . , where the die material movement gap 1
2 is narrowed to close to the desired pipe diameter. At _D5 , the heating temperature is lowered to near the melting point of the resin, and the process moves to the next heat insulation zone 8.

The heat insulation zone 8 is continuous from the heating melting zone 7,
It has a die structure equipped with an adiabatic air cooling device 13. Here, approach the dimensions of the inner and outer cylinders of the pipe, D ₄ ~ _{D 5}
It is a resin curing part that prevents the generation of air bubbles that may remain in the compression zone and "nests" caused by cooling, and also acts as an inter-device heat insulating part between it and the next cooling zone 9. . Since this heat insulation zone is the part where the resin passes through its melting point and is cooled, the same effect can be obtained even if natural air cooling is used, as long as the drawback that the length of the die is long is tolerated.

The cooling zone 9 has a die structure including a water-cooled forced cooling device continuous from the heat insulation zone 8 . In the example shown in Fig. 2, the water-cooled forced cooling system is divided into F ₁ to F ₃ by an outer cylinder jacket 14 divided into three parts, and an inner cylinder jacket 15 is provided inside the inner cylinder. The structure is such that the resin molded product is forcibly cooled by flowing water. The length of the cooling zone 9 is relatively long and is approximately the same as that of the heating and melting zone, and this portion substantially controls the shape of the molded product and also completes cooling. However, if the molded product is thick, the inside of the molded product will not be cooled, and the moving speed of the resin will increase, which may cause the pressure inside the die to drop below the specified value. Therefore, a pressure correction zone 10 was provided at the tip of the extruder to reduce the outer size of the extruded product in conjunction with the pressure inside the die.

The pressure straightening zone 10 is provided at the tip of the die of the cooling zone 9, and in this example, a plurality of two-part flange-shaped dies 17 are provided around the outer periphery of the molded product 16 as shown in FIG. The device is an automatic device that changes the restriction of the inner diameter of the die 17 in response to changes in the internal pressure of the die. By providing this die 17, the dimensional accuracy of the molded product 16 is improved, and a stable thick product can be obtained continuously.

Ultra-high molecular weight polyethylene thick-walled molded products are produced under the extrusion conditions described above, but the extrusion speed of the product is extremely slow at 0.15 to 10 m/hr, and the wall thickness of the molded product is large. The larger the diameter, the slower the extrusion speed. But 0.15
Speeds below m/hr are generally uneconomical and impractical. On the other hand, if the length exceeds 10 m, the resin will not be fully melted and undissolved substances and bubbles will remain inside, resulting in a thick molded product with poor surface gloss, which is not desirable, so it is necessary to set it within the above conditions. be.

The present invention will be explained in more detail below with reference to Examples.

Example Hi-Zex Million (registered trademark, manufactured by Mitsui Petrochemical Industries, Ltd.) 240M powder (average particle size 200 μm) was used as a raw material for ultra-high molecular weight polyethylene. The average molecular weight of this substance is approximately 1 million by the viscosity method.
It is said to be about 3 million by light scattering method.

The extrusion molding machine is shown in Figures 1 and 2,
Its specifications and extrusion conditions are as follows.

Cylinder zone Screw outer diameter 50mmφ Screw effective length L/D=20 Flight pitch 50mm constant C ₁ 270℃ C ₂ 260℃ Heating melting zone Pressure 65Kg/cm ² D ₀ 260℃ D ₁ 260℃ D ₂ 260℃ D ₃ 230℃ D ₄ 200℃ D ₅ 170℃ Insulation zone 140℃ Cooling zone F ₁ Water input 50℃, water output 53℃ F ₂ Water input 30℃, water output 32℃ F ₃ Water input 18℃, water output 19℃ Die outer diameter 150mm Die inner diameter 110mm The molded product obtained at an extrusion speed of 1800 mm/hr or more was a thick continuous round pipe with a resin layer thickness of 18 mm and an outer diameter of 148 mm, which was cut into lengths of 600 mm. A metal pipe was then press-fitted into the inside, and the roller was completed as a roller for a roller conveyor used to transport cold-rolled steel plates and shaped steel at a steelworks.

The extrusion speed in this device is 0.15 to 10 m/hr, which seems extremely slow compared to a normal extruder, but
Conventional molding of ultra-high molecular weight polyethylene thick materials is press molding, and in the case of thick-walled pipes in particular, the manufacturing method involves drilling holes inside the cylindrical molded material by machining, which is much more efficient than this method. was at fault.

Furthermore, with press working, it is difficult to manufacture pipes and plates of free dimensions, but the present method and apparatus allow continuous extrusion molding, and are therefore extremely superior in this respect as well.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of the cylinder zone, and FIG. 2 is a longitudinal sectional view of the main part of the extruder. 1... Cylinder zone, 6... Extruder main body,
7... Heat melting zone, 8... Heat insulation zone, 9...
...Cooling zone, 10...Pressure correction zone, 16...
...Molded product, 17...Flanged die.

Claims (1)

[Claims] 1 Ultra-high molecular weight polyethylene powder with an average molecular weight of 500,000 or more is heated at a high temperature above its melting point to form granules containing air inside, and then heated to a pressure of 150,000 yen.
~200Kg/ ^cm2 , ultra-high molecular weight polyethylene that is press-fitted into a mold under high pressure and high temperature of 160~330℃, melted, extruded from a molding nozzle, and formed into thick-walled pipes, thick plates, etc. Continuous molding method for meat molded products. 2 Consists of a cylinder zone, heat melting zone, heat insulation zone, cooling zone and pressure straightening zone, the cylinder zone is a screw conveyor heated to a high temperature higher than the melting point of ultra-high molecular weight polyethylene, and the heat melting zone is a screw conveyor heated to a temperature of 330℃~ It has a die structure that is equipped with an external heater that provides a temperature gradient from high temperature to low temperature between 160℃ and pressurizes in the range of 15 to 200Kg/ ^cm2 , and the adiabatic zone is an adiabatic air cooling device that is continuous from the heating melting zone. The cooling zone is a die structure equipped with a water-cooled forced cooling device that is continuous from the adiabatic zone, and the pressure correction zone is provided at the tip of the cooling zone die, and is a split die that forms the outer periphery of the molded product. Continuous molding equipment for ultra-high molecular weight polyethylene thick-walled molded products, which is a variable die that is linked to the internal pressure of the heat-melting zone die.