JPS5841733B2 - Extrusion molding method for crosslinked hollow bodies of polymeric materials - Google Patents

Description

[Detailed Description of the Invention] As a method for obtaining a hollow molded body of a polymer material, there is a method in which gas (mostly air) is pressurized into the hollow interior, and the shape is maintained by a shaping die outside the hollow body and cooled and solidified. be.

At this time, the role played by the gas is to apply static pressure to the inner surface of the hollow body discharged from the forming die and to uniformly distribute the outer surface of the hollow body on the inner wall of the forming die, which has a cooling function, in order to obtain a good hollow formed body. The purpose is to make the shape, surface condition, and physical properties uniform by bringing the materials into contact with each other under a certain pressure.

Therefore, the gas is allowed to flow in or out through the perforations provided in the shaping die at room temperature or in a cooled state.

Particularly when molding thick walls or materials with relatively low viscosity, the hollow body must be cooled quickly after being discharged from the shaping die to prevent the hollow body from sagging. In addition to cooling, forced circulation of room temperature or cooled gas is often used in combination.

However, in order to produce a crosslinked hollow body of a polymeric material, a step is required to allow the crosslinking reaction to proceed and complete during or after the final shaping process.

Therefore, contrary to the production of hollow molded bodies made of polymeric materials as described above, it is necessary to heat the hollow molded bodies during or after the final shaping process.

Conventionally, as a means of achieving such a crosslinking reaction by heating, a heater is provided in the blow molding die, which is the final shaping path, and a heater is also provided in the inside mandrel, so that both sides of the blow molding die and the inside mandrel are heated. A method is adopted in which the crosslinking reaction is completed in the excipient path by actively heating the material.

However, with this method, if the extrusion speed is high, the molded product wall thickness is large, or the molded product outer diameter is small, it becomes necessary to lengthen the molding die and inside mandrel in order to complete the crosslinking reaction, and the crosslinking reaction As this progresses, the fluidity of the polymeric material decreases significantly, resulting in deflection, stagnation, etc. inside the shaping die.

As a result, the quality of the blow molded product becomes non-uniform, and there are disadvantages such as the surface being particularly deteriorated, and the production speed and the setting of the shape and dimensions of the molded product are restricted.

In order to eliminate these drawbacks, attempts have been made to inject lubricating fluid into the inner and outer surfaces of the hollow body flow path to smooth the flow of the polymer material.

However, even with the use of lubricating fluids, it is extremely difficult to obtain molded products of good quality.

The present invention provides a method for continuously molding a crosslinked hollow body without causing the above-mentioned disadvantages and obtaining a good crosslinked hollow body.

That is, in the present invention, a polymer material mixed with a crosslinking agent is melted and kneaded using an extruder such as a screw to reach a desired resin temperature, and then introduced into a blow molding die to form a hollow body. Instead of completing the crosslinking reaction at the end of the excipient, the crosslinking reaction is allowed to proceed to a certain extent during the excipient path, or is not allowed to proceed and is then completed after the excipient leaves the excipient path.

Therefore, in order to advance the crosslinking reaction as described above, the present invention decomposes the crosslinking agent in the melt from outside the blow molding die through an inflow passage and an outflow passage bored in the inside mandrel of the blow molding die. The hollow body has a means for internally heating a hollow body having a viscosity such that it can maintain a hollow shape without the support of the hollow die or the inside mandrel by injecting a fluid heated to a certain temperature.

If the viscosity of the melt mixed with a crosslinking agent is increased by allowing the crosslinking reaction to proceed in the middle of the blow molding die, the hollow shape can be maintained even when the melt is separated from the blow molding die. The temperature to drive the crosslinking reaction to completion is applied via a heated fluid flowing through the inside mandrel.

However, if the material to be molded by the blow molding die has a high molecular weight or the crosslinking reaction rate is high, the crosslinking reaction may not proceed during the forming path, and the crosslinking may be carried out using the heated fluid as described above after leaving the forming path. It is also possible to drive the reaction to completion.

The hollow body that exits the hollow molding die is annealed tube, which maintains the hollow shape and completes the crosslinking reaction.
The hollow body may be introduced into an annealing tube in which the crosslinking reaction is completed while being expanded or withdrawn.

Furthermore, the crosslinking reaction may be completed while the hollow body exiting the blow molding die is expanded in the atmosphere by providing a predetermined heating device externally, or the crosslinking reaction may be completed while the hollow body is extruded into a pressurized fluid. It is also possible to drive the reaction to completion.

In either case, any fluid can be used to press into the hollow body as long as it does not decompose at a temperature sufficient to promote the crosslinking reaction of the hollow body and does not suppress the crosslinking reaction. can.

For example, air, oil, surfactant solution, inert gas, etc. can be used, but it is desirable to select an appropriate one depending on the use of the hollow body.

N2 gas is extremely effective in preventing contamination inside the hollow body and at the same time improving crosslinking efficiency.

Next, the present invention will be explained in detail based on the accompanying drawings.

1 to 4 are cross-sectional views of essential parts of an apparatus for carrying out the present invention, showing aspects of hollow body molding and progress of crosslinking reaction according to the present invention.

That is, in FIG. 1, a polymer material mixed with a crosslinking agent is melt-kneaded using an extruder 1 at a temperature and pressure that does not cause a crosslinking reaction.
After the temperature is instantaneously raised to a temperature at which the crosslinking reaction occurs and progresses in the orifice chair 2 connected to the extruder 1,
It is introduced into the hollow molding die 3.

Inside the blow molding die 3, an inside seven mandrel 4 is disposed, and the inside mandrel 4 is provided with an inlet passage 5 and an outlet passage 6 for heated and pressurized fluid.

The polymer material introduced into the blow molding die 3 is guided into the flow path formed by the blow molding die 3 and the inside mandrel 4, and is shaped into the final molded product shape. The crosslinking reaction further progresses due to the heating by the heater 7 and the heat of the heated pressurized fluid applied through the inflow path 5 and outflow path 6 of the inside 7 well 4.

then adjacent to the blow-forming die 3 and blow-forming-die 3;
The heating medium liquid pressure-injected from the porous annular body 8 having the same inner diameter as the flow path covers the outer peripheral surface of the hollow body 9, and the hollow body 9 enters a plug flow state.

Then, when the hollow body 9 is passed through the internal passage of the annealing tube 10, which has the porous annular body 8 in a part and has the same shape and dimensions as the hollow molding die 3, the annealing tube The heater 11 provided around the outer periphery of the hollow body 9 and the heated pressurized fluid circulating inside the hollow body 9 actively heat the hollow body from the inner and outer surfaces to complete the crosslinking reaction.

The hollow body 9 in which the crosslinking reaction has been completed is an annealing tube 1
The cooling jacket 12 provided on the outer circumference of the rear end of the
After being slowly cooled, it is extruded into the atmosphere.

Here, the heated pressurized fluid is press-fitted into the hollow body 9 from the inflow passage 5 at the tip of the inside mandrel 4, and after imparting heat to the hollow body 9, it passes through the outflow passage 6 inside the inside mandrel 4 again. is returned to an external heat exchanger (not shown),
It is heated again and circulated to keep the inside of the hollow body 9 at a constant temperature to complete the crosslinking reaction.

FIG. 2 shows an example in which the inner diameter of the annealing tube is larger than the inner diameter of the flow path of the blow molding die.

That is, the hollow body 13 is shaped in the flow path formed by the hollow molding die 3 and the inside mandrel 4, and is brought into a state of plug flow by the heating medium liquid press-filled from the porous annular body 8.
is expanded in the radial direction by the pressure of the heated pressurized fluid in the annealing tube 14, which has an inner diameter larger than the channel inner diameter of the hollow molding die 3, until it comes into contact with the inner opening ζ of the annealing tube 14.

When the hollow body 13 is expanded in the annealing tube 14, the hollow body 13 is slightly distorted because the crosslinking reaction has already progressed and the hollow body 13 has rubber-like elasticity.

Next, the hollow body 13 is actively heated from the inside and outside by the heater 15 provided on the outer periphery of the annealing tube 14 and the heated pressurized fluid circulating inside the hollow body to complete the crosslinking reaction.

Thereafter, it is slowly cooled by a cooling jacket 16 provided on the outer periphery of the rear end of the annealing tube 14, and then extruded into the atmosphere.

In this molding method, the molded product has elastic memory, so it can be used as a shrink tube by heating it again.

FIG. 3 is an example in which the hollow body is expanded in the atmosphere and the crosslinking reaction is completed without using an annealing tube.

That is, the hollow body 1T shaped by the flow path formed by the hollow molding die 3 and the inside mandrel 4 is the hollow body 17.
The infrared heater 1 is expanded in the atmosphere by the heated pressurized fluid circulating inside and is disposed outside the hollow body 17.
Coupled with the heating action in step 8, the crosslinking reaction progresses to completion.

Note that the infrared heater 18 is provided on the side wall 19 so that the heating effect on the hollow body 17 is sufficiently exerted.

In the molding method shown in FIG. 3, the hollow body 17 expands during the progress of the crosslinking reaction, and by cooling after the reaction is completed, a heat-shrinkable tube utilizing the elastic memory effect can be obtained, but the crosslinking reaction progresses. A thermal expansion tube can also be obtained by drawing it down midway.

FIG. 4 shows an example in which a hollow body is extruded into a heated and pressurized fluid.

Depending on the type of crosslinking agent mixed into the polymeric material, by-product gas may be generated during the crosslinking reaction.

For example, in the combination of low density polyethylene and DCP, generation of by-product gas is observed.

However, the molding method shown in FIG. 4 can sufficiently suppress voids due to the generation of by-product gas.

That is, the hollow body 20 shaped by the flow path formed by the hollow molding die 3 and the inside mandrel 4 is extruded into a heated pressurized fluid, and the heated pressurized fluid circulating inside the hollow body 20 and the hollow body 20 are extruded into a heated pressurized fluid. The crosslinking reaction progresses and is completed by heating the heating fluid press-in from the outside and the infrared heater 30.

Various heating fluids can be used as the heating fluid pressurized from the outside of the hollow body 20, similar to the heating fluid pressurized through the inside mandrel 4, but gases, especially N2 gas, are effective from the viewpoints of contamination prevention and crosslinking efficiency. .

The pressure of the heated fluids pressurized into the inside and outside of the hollow body 20 is detected by the pressure detector 2L22, and maintained at a desired level via a controller (not shown).At the same time, the pressure of both fluids is detected by the temperature detectors 23 and 24. The temperature is detected and controlled to a predetermined temperature.

In this way, the heated fluid pressurized into the inside and outside of the hollow body 20 is maintained at a predetermined pressure and temperature, and even when the crosslinking reaction of the hollow body 20 is completed, a uniform hollow body without voids can be obtained. .

Furthermore, by appropriately adjusting the pressure and temperature of the heated fluid that is pressurized into and out of the hollow body 20, expansion or withdrawal of the crosslinked hollow body can be selected, and the degree thereof can also be determined.

In the figure, 31 is a seal packing, 32 is a cooling jacket, and 33 is a reaction chamber wall.

The hollow body in which the crosslinking reaction has been completed by the various methods described above is extruded into the atmosphere and then wound up in the process shown in FIG.

To explain the molding method shown in FIG. 1 as an example, the hollow body is slowly cooled in the cooling device 25 to a temperature at which it can still be sufficiently deformed, and the inside of the hollow body is heated in a pair of take-off rollers 27 and 28 of the take-off machine 26. The pressurized fluid is pressed and taken up while maintaining its pressure, and then wound onto a reel 34 in a winder 29 .

As described above, in the present invention, the crosslinking reaction does not proceed, or only slightly proceeds, in the flow path formed by the blow molding die and the inside mandrel.
The hollow molding die and the inside mandrel can be shortened, and the surface condition of the hollow body can be made smooth.

Furthermore, the hollow body is pressurized by a heated fluid that is injected into the hollow body: The heating action makes the crosslinking distribution of the hollow body uniform,
In other words, it is possible to achieve uniform quality, improve productivity, and increase the degree of freedom in forming shrinkable tubes or expansion tubes that utilize the elastic memory effect, and the dimensions of the hollow body can also be changed using a blow molding die. is not limited to the flow path of
It can be taken arbitrarily.

Comparative example High density polyethylene 7 (MI=0.3, density 0.96)
2,5-dimethyl- as a crosslinking agent per 100 parts by weight
2,5-di(1-butylperoxy)hexyne-3 to 1
Parts by weight were mixed, and this was formed into a hollow body using the apparatus shown in Figure 1, and N2 gas at 18°C was passed through the inflow and outflow channels of the inside mandrel at 5 Ky/crri.
The sample was press-fitted into the hollow body under the conditions of ', passed through an annealing tube heated to 230°C, and after being subjected to δ-conversion at the inner end of the annealing tube, it was released into the atmosphere.

The average crosslinking rate of the obtained hollow body was 23 coefficients, and the crosslinking rate near the surface of the hollow body was 80 coefficients, while that near the inside was 3 to 3.
It was 5 rice cakes.

Moreover, the surface of the hollow molded body was slightly inferior in smoothness, and especially the inner surface had wavy irregularities.

Example high density polyethylene (M I = 0.3, density 0.9
6) 2,5-dimethyl-2,5-di(1-butylperoxy)hexyne-3 as a crosslinking agent per 100 parts by weight
1 part by weight was mixed with 1 part by weight, and this was formed into a hollow body through a blow molding die using the apparatus shown in Fig. 1. At the same time, 5Kt/N2 gas heated to 230°C was passed through the inflow and outflow channels of the inside mandrel. It was press-fitted into the hollow body under crri' conditions to complete the crosslinking reaction.

The obtained hollow body was a uniformly crosslinked molded body with a crosslinking rate of 80, and both the inner and outer surfaces were smooth.

Example 2 High-density polyethylene mixed with a crosslinking agent was mixed in the same manner as in Example 1, and this was formed into a hollow body through a blow molding die using the apparatus shown in Fig. 2, and the inflow and outflow channels of the inside mandrel were formed. NJ gas heated to 235° C. was injected into the hollow body through the channel under conditions of 5 Kt/crrkD to complete the crosslinking reaction.

The obtained hollow body was a uniformly crosslinked molded body with a crosslinking rate of 83, and could be used as a shrinkable tube by heating it again.

[Brief explanation of the drawing]

1 to 4 are cross-sectional views showing essential parts of an apparatus for implementing the present invention, and FIG. 5 is a diagrammatic explanatory view schematically showing all steps of the present invention. 3...Blow molding die, 4...Inside mandrel 8...Porous annular body, 9,13.17.20...Hollow body, 10,14...Annealing tube, 18°30, , infrared heater, 2L22...pressure detector,
23, 24... Temperature detector, 26... Taking machine, 2
9... Winding machine.

Claims (1)

[Scope of Claims] 1. A method for molding a hollow body by introducing a melt of a polymeric material mixed with a crosslinking agent into a blow molding die, which comprises: A fluid heated to a temperature capable of decomposing the crosslinking agent in the melt is injected from the outside of the hollow molding die through the outlet passage to an extent that the hollow shape can be maintained without the support of the hollow molding die or the inside mandrel. 1. A method for extrusion molding a crosslinked hollow body made of a polymeric material, characterized in that the hollow body having a viscosity of . 2. A method for extrusion molding a crosslinked hollow body made of a polymeric material according to claim 1, wherein the crosslinked hollow body is taken out while being pressed and closed, and a heated fluid press-fitted into the hollow body is circulated. 3 An annealing tube is provided adjacent to the hollow molding die, and a heating medium liquid is pressurized from the joint part to the contact interface between the hollow body and the annealing tube, and the hollow body is extruded in a plug flow state while the lees annealing is performed. Extrusion molding of a crosslinked hollow body made of a polymeric material according to claim 1 or 2, which is heated to a temperature that actively decomposes the crosslinking agent in the hollow body by a heater provided on the outer periphery of the tube. Method. 4. A method for extrusion molding a hollow body of a crosslinked polymeric material according to claim 3, wherein an annealing tube having the same size and shape as the die is provided adjacent to the hollow molding die. 5. A method for extrusion molding a crosslinked hollow body of a polymeric material according to claim 3, wherein an annealing tube having a size or shape larger or smaller than that of the die is provided adjacent to the hollow molding die. . 6. A method for extrusion molding a crosslinked hollow body made of a polymeric material according to claim 1 or 2, wherein the hollow body extruded from a blow molding die is allowed to complete a crosslinking reaction in the atmosphere. 7. A crosslinked hollow body made of a polymeric material according to claim 1 or 2, which is extruded from a blow molding die into a heated pressurized fluid whose temperature and pressure are controlled to predetermined levels. Extrusion method. 8. Claims 1, 2, 6, or 7, in which the hollow body extruded from the blow molding die is heated by infrared irradiation from the outside or inside to complete the crosslinking reaction. A method for extrusion molding a crosslinked hollow body of a polymeric material according to any one of the above.