JPS6254651B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing ultra-high molecular weight polyethylene pipes and a pipe-forming die. Ultra-high molecular weight polyethylene with a molecular weight of 1,000,000 or more has excellent impact resistance, abrasion resistance, self-lubricating properties, chemical resistance, etc., and is widely used as an engineering plastic. However, compared to general-purpose resins, the melt viscosity is extremely high and the fluidity is poor, so it is extremely difficult to mold using normal extrusion molding or injection molding. Therefore, molding is generally performed using compression molding. There is a pipe,
It is almost impossible to mold long objects such as rods by compression molding. A ram extruder equipped with a mandrel (Japanese Patent Application Laid-Open No. 1983-28896) has been proposed as a device for continuously manufacturing ultra-high molecular weight polyethylene pipes, but the ram extruder has problems such as inferior molding speed and poor thickness unevenness accuracy. It has the following disadvantages. Improving the molding speed can be achieved by using a screw extruder, but as mentioned above, ultra-high molecular weight polyethylene has an extremely high melt viscosity and poor fluidity, so it is not possible to adjust the uneven thickness with a general-purpose resin pipe molding die. , resin fusion is insufficient, and sizing (outer diameter or inner diameter regulation) cannot be done using a normal vacuum former or internal pressure.Furthermore, if it is rapidly cooled, internal stress remains and physical properties deteriorate, so it is difficult to manufacture good pipes. That was difficult. Therefore, the present inventors
As a result of studying the development of a pipe-forming die that can be molded using a normal screw extruder, it was discovered that a special die consisting of a heating die and a cooling sizing die was suitable for manufacturing ultra-high molecular weight polyethylene pipes, and the present invention was completed. I came to the conclusion. That is, in the present invention, ultra-high molecular weight polyethylene is melted in a screw extruder, dispersed in a breaker plate, heated and compressed between a spider die and a heating die inlet, and adjusted for uneven thickness, and heated at 250 to 150°C in a heating die. A method for producing an ultra-high molecular weight polyethylene pipe, characterized in that the pipe is fused while gradually lowering the temperature in the range of 100°C to room temperature, and then cooled and solidified in a tapered cooling sizing die while gradually lowering the temperature in the range of 100°C to room temperature. From the extruder side, the ratio (S ₁ /S ₂ ) of the cross-sectional area S ₁ of the resin flow path at the breaker plate, spider die, and spider die connection area to the cross-sectional area S ₂ of the resin flow path at the heating die connection area is 2 or more. 5 and a tapered die equipped with a thickness unevenness adjustment ring at the heating die connection part, a heating die with L/D of 1 to 10, and L/D of 1 to 10, and a cross-sectional area S of the resin flow path at the connection part with the heating die. ₃ and the cross-sectional area S ₄ of the resin flow path at the exit of the tapered cooling sizing die (S ₃ /S ₄ ) is 1.01 to 1.5, and the diameter of the mandrel with the heating die φ _{3 and the cross-sectional area S 4} of the exit of the tapered cooling sizing die are 1.01 to 1.5. Ratio to mandrel diameter φ (φ ₃ /φ ₄ )
The present invention provides a pipe forming die characterized in that it is composed of a tapered cooling sizing die with a diameter of 1.01 to 1.5. The ultra-high molecular weight polyethylene used in the present invention usually has an intrinsic viscosity [η] of 10 dl/g or more, preferably 15 dl/g or more, as measured in a decalin solvent at 135°C, and has a melt flow rate (ASTM D 1238F).
0.01g/10min or less of ethylene homopolymer or ethylene with other α-olefins such as propene, 1-butene, 1-hexene, 1-octene, 4-methylene-1-pentene, etc. It is a crystalline copolymer. The method of the present invention involves melting the ultra-high molecular weight polyethylene in a screw extruder at a temperature of usually 150 to 250°C, dispersing the molten resin through a breaker plate, and heating and compressing it between a spider die and a heated die inlet, preferably Heat compression is performed at a compression ratio of 2.0 to 4.0 to adjust the uneven thickness, and the temperature is successively lowered in a heating die to 250 to 150°C, preferably 220 to 170°C, followed by melting in a tapered cooling sizing die. While gradually lowering the temperature inside the pipe from 100°C to room temperature, preferably from 80°C to room temperature, it is particularly preferable to sequentially lower the temperature on the outside of the pipe from 100°C to room temperature, and at the same time, lower the temperature on the inside of the pipe to 100°C to room temperature. This is a method of cooling and solidifying pipes at room temperature, with a temperature difference of at least 10°C between the outside and inside of the pipe.This method produces ultra-high quality pipes with beautiful skin on both the outside and inside, and with little unevenness in thickness or thinness. A molecular weight polyethylene pipe is obtained. The ultra-high molecular weight polyethylene melted in a screw extruder is in the form of a ribbon, and even if it is introduced directly into a die, it is difficult to obtain a pipe with a uniform thickness, and it is necessary to disperse it using a breaker plate. Unlike the melt of general-purpose resin, the melt of ultra-high molecular weight polyethylene is in the form of drops, and it is heated between the spider die and the heating die inlet to erase spider marks (weld lines) caused by the breaker plate and spider die. Needs to be compressed. If heating and compression between the pipes is insufficient, the fusion of the molten material will be insufficient, leaving weld lines, or in severe cases, no fusion will occur at all, making it impossible to obtain a homogeneous pipe. The uneven thickness of the pipe is adjusted before the heated and compressed molten resin enters the heating die. It is very difficult to adjust thickness unevenness by moving the outer die as with general-purpose resins because the melt viscosity of ultra-high molecular weight polyethylene is extremely high. Note that the heating die is a die that completely fuses the molten resin and slowly lowers the temperature before introducing it into the cooling sizing die. Forcibly moving the outer die to adjust the uneven thickness will affect the flow of the resin. This is not desirable as it may cause disturbance. The molten resin that has been adjusted for uneven thickness is fused in a heating die while gradually lowering the temperature in the range of 250 to 150℃, but when the temperature at the entrance of the heating die is 250℃.
If it exceeds .degree. C., the resin pressure will become excessive and the temperature difference between the resin and the cooling sizing die will become extremely large, so the resin will be rapidly cooled and internal stress will remain, which is not preferable. On the other hand, if the temperature at the heating die inlet is lowered to less than 150°C, insufficient fusion will occur. If the temperature of the heating die is lowered suddenly instead of gradually, internal stress may remain in the pipe and cause it to break during use. Furthermore, if the width of the temperature drop is made larger than necessary, the heating die becomes longer and the pressure inside the die becomes excessive, which is also economically undesirable. Sizing of pipes fused with a heating die is done by cooling and solidifying the pipes in a tapered cooling sizing die by sequentially lowering the temperature from 100℃ to room temperature, but if the cooling temperature exceeds 100℃, the cooling time becomes longer. If the temperature at the cooling sizing die inlet falls below 50°C, the pipe will cool rapidly and internal stress will remain in the pipe. In addition, the temperature on the outside of the pipe is gradually lowered from 100°C to room temperature, and the inside of the pipe (inside the mandrel) is cooled at 100°C to room temperature, and the cooling temperature on the outside and inside of the pipe is at least 10°C or higher. Differential cooling allows the resin inside the die to rotate, making it possible to manufacture pipes with extremely high thickness unevenness accuracy. In addition, by using a heating die and a tapered cooling sizing die whose resin passages are coated with fluororesin or silicone resin, it is possible to lower the resin pressure and create a pipe with smoother skin on the inner and outer surfaces of the pipe. can be obtained. Next, an embodiment of a pipe-forming die suitable for manufacturing ultra-high molecular weight polyethylene pipes will be described based on the drawings. The pipe forming die of the present invention includes, from the extruder (not shown) side, a breaker plate 1, a spider die 2, and a cross-sectional area of the resin flow path at the spider die connection part.
The ratio of S ₁ to the cross-sectional area S ₂ of the resin flow path at the heating die connection portion (S ₁ /S ₂ : compression ratio) is 2 to 5, preferably 2.
4 and heating die connection part with uneven thickness adjustment ring 4
, a heating die 5 with L/D of 1 to 10 (L represents the length of the land of the die, and D represents the inner diameter of the die (corresponding to the outer diameter of the pipe)), and L/D of 1 to 10. 10, preferably the ratio of the cross-sectional area S ₃ of the resin flow path at the connection part with 2 to 7 and the heating die 5 to the cross-sectional area S ₄ of the resin flow path at the outlet of the tapered cooling sizing die (S ₃ /S ₄ ) is 1.01 to 1.5, preferably 1.01 to 1.1, and the ratio of the diameter φ ₃ of the mandrel at the connection part with the heating die 5 to the diameter φ ₄ of the mandrel at the outlet of the tapered cooling sizing die (φ ₃ /
It consists of a tapered cooling sizing die 6 with a diameter of 1.01 to 1.5 (φ ₄ ). The breaker plate 1 is for dispersing and regulating the flow of the melted ultra-high molecular weight polyethylene extruded into a ribbon shape by a screw extruder, and it is especially useful if the breaker plate has holes uniformly throughout. There are no limitations. However, if the holes are too small or unevenly distributed concentrically, the resin pressure may become high.
This is not desirable because it is not dispersed. The breaker plate 1 is normally used by being fitted into a die body 21. The spider die 2 includes a mandrel 22, a mandrel 8, and a mandrel 10 that regulate the inner diameter of the pipe.
It supports the spider and usually has three or more spiders. The taper die 3 heats and compresses the molten resin separated by the spider die 2 before guiding it to the heating die 5.
This is a die that erases spider marks (weld lines), and if the compression ratio (S ₁ /S ₂ ) is less than 1, the spider marks will not disappear. Also, compression ratio (S ₁ /S ₂ )
If it exceeds 5, the resin pressure becomes excessive and extrusion molding of the pipe becomes difficult. The thickness unevenness adjustment ring 4 is a device that adjusts the thickness unevenness of the molten resin heated and compressed by the taper die 3, and the adjustment is performed using bolts 41. Adjustment of uneven thickness of general-purpose resin is performed by moving the outer die 31, but since the viscosity of the molten ultra-high molecular weight polyethylene is extremely high, it is difficult to adjust the uneven thickness using the outer die 31. If a thickness adjustment ring is provided, the ring will obstruct the uniform flow of the molten material, which is undesirable as it will cause cracks in the resulting pipe. Furthermore, since the general-purpose resin has a low melt viscosity, even if thickness unevenness adjustment is performed using the thickness unevenness adjusting ring 4, it is meaningless because the width of the resin flow path in the heating die 5 becomes the same. If the L/D of the heating die 5 is less than 1, the molten ultra-high molecular weight polyethylene will not be sufficiently fused, and
If the temperature cannot be lowered to a predetermined level and L/D exceeds 10, there will be no problem in terms of physical properties, but this is not preferable because the resin pressure in the die will increase and a long die will be required. The heating device 51 of the heating die 5 adjusts to at least two or more temperatures in order to sequentially lower the temperature of the extruder and fuse the ultra-high molecular weight polyethylene melt in the heating die at a temperature higher than the melting point. You need to be able to do it. It should be noted that coating the resin channels of the outer die 7 and the mandrel 8 with a fluororesin or a silicone resin is effective in improving the appearance (skin) of the extruded pipe and improving the extrusion stability. The heating die 5 may be a straight die, but may also be a tapered die with a narrow side on the sizing die 6 side. Further, the heating die 5 may be formed from two or more blocks as long as the above conditions are satisfied. L/D of tapered cooling sizing die 6 is 1
If L/D is less than 10, it is not sufficient to slowly cool the molten ultra-high molecular weight polyethylene.On the other hand, if L/D exceeds 10, it will not affect the physical properties, but the resin pressure in the die will increase, and This is not preferable because it requires a die. A device 6 that cools the outside of the pipe, that is, the outer die 9 with the cooling device of the sizing die 6
1, it is necessary to divide the melt into at least two parts in order to slowly cool the melt. The outer die 9 can be cooled by introducing a cooling liquid such as water or ethylene glycol through the water inlets 23 and 24. The introduced coolant is discharged from drain ports 25 and 26, respectively. Inside 81 of mandrel 10
By allowing the resin to be cooled by cooling air using the air nozzle 34, the resin in the resin flow path can be rotated, and a pipe with better thickness unevenness accuracy can be manufactured. If S ₃ /S ₄ is less than 1.01 and φ ₃ /φ ₄ is less than 1.01, the cooled and solidified resin clings to the mandrel 10, increasing the motor load of the extruder and making it impossible to mold. On the other hand, S ₃ /S ₄
If it exceeds 1.5 and φ ₃ /φ ₄ exceeds 1.5, the resistance with the outer die 9 will increase and molding will not be possible. In addition, if the resin channels of the outer die 9 and the mandrel 10 are coated with fluororesin or silicone resin,
It is effective in improving the appearance (skin) of extruded pipes and reducing resin pressure. In addition, the tip 1 of the mandrel 10
It is preferable to let the pipe 1 out from the outer die 9 so that the tip of the extruded pipe does not get caught inside. Example 1 [η] is 17 dl/ as ultra-high molecular weight polyethylene
g, with a melt flow rate of less than 0.01 g/10 min (product name Hi-Zex Million 240M,
Mitsui Petrochemical Industries, Ltd.) was melted in a 65mmφ single-screw extruder (temperature set at 210°C), and the temperature of each of the breaker plate 1, die body 21, spider 2, and taper die 3 was set at 200°C to prevent uneven thickness. is adjusted by the bolt of the thickness unevenness adjustment ring 4. The molten resin with uneven thickness adjusted in this way is heated to 200°C by heating die 5.
The temperature was gradually lowered from then on until it reached 170°C at the die exit. The temperature of this was sequentially lowered from the inside and outside using a tapered cooling sizing die 6, and a pipe with a pipe surface temperature of 60° C. was obtained at the die exit. The thickness deviation accuracy of the obtained pipe was 9.2 ⁺⁰ . ^3-0 _mm , the appearance is very good, and the mechanical strength is also as shown in the table.
The values were exactly the same as those of the press sheet shown for reference, and a pipe with excellent properties was obtained. The dimensions of the obtained pipe are 98.5 mm in outer diameter and 98.5 mm in inner diameter.
The average wall thickness was 79.2 mm and 9.2 mm. 【table】

[Brief explanation of the drawing]

The figure is a side sectional view of the pipe-forming die of the present invention. 1... Breaker plate, 2... Spider die, 3... Taper die, 5... Heating die, 6
...Taper type cooling sizing die.

Claims (1)

[Scope of Claims] 1. Ultra-high molecular weight polyethylene is melted in a screw extruder, dispersed in a breaker plate, heated and compressed between a spider and the inlet of a heating die, and adjusted for thickness deviation, and then heated to a thickness of 250 to 150 in the heating die. Production of ultra-high molecular weight polyethylene pipe characterized by fusing while lowering the temperature sequentially in the range of 100°C to room temperature, followed by cooling and solidifying in a tapered cooling sizing die while lowering the temperature sequentially in the range of 100°C to room temperature. Method. 2. Cooling and solidification in the taper-type cooling sizing die is performed by sequentially lowering the temperature from the outside of the pipe in the range of 100°C to room temperature, cooling the inside of the pipe to 100°C to room temperature, and cooling the inside of the pipe between the outside and inside of the pipe. 2. The method according to claim 1, wherein the cooling is performed with a temperature difference of at least 10°C. 3 From the extruder side, the ratio (S ₁ /S ₂ ) of the cross-sectional area S ₁ of the resin flow path at the breaker plate, spider die, and spider die connection portion to the cross-sectional area S ₂ of the resin flow path at the heating die connection portion is 2 to 5 and a tapered die equipped with a thickness unevenness adjustment ring at the heating die connection part, L/D is 1
~10 heating dies, L/D is 1 to 10, and the ratio of the cross-sectional area _S3 of the resin flow path at the connection part with the heating die to the cross-sectional area _S4 of the resin flow path at the exit of the tapered cooling sizing die (S ₃ /S ₄ ) is 1.01 to 1.5, and the ratio of the mandrel diameter φ ₃ at the connection part with the heating die to the mandrel diameter φ ₄ at the outlet of the tapered cooling sizing die (φ ₃ /φ
₄ ) A pipe forming die comprising a tapered cooling sizing die having a diameter of 1.01 to 1.5. 4. The die according to claim 3, wherein the mandrel of the cooling sizing die is longer than the outer die.