JPS6359857B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for controlling the temperature of a pipe-like material that can be applied to an oriented pipe forming machine.

Pipes have a variety of uses, such as pipes for transporting materials or cans as containers, but recently the demand for plastic pipes has been rapidly increasing due to their corrosion resistance and weight reduction, especially polyester, polyethylene, and polypropylene. Can-shaped containers such as these are desirable from the point of view of food hygiene.

However, conventional plastic pipes are made by melting and kneading the raw material plastic using an extruder.
A pipe-shaped product was extruded from a pipe die and then cooled and solidified. In plastic pipes formed in this way, the higher-order structure of the molecular chains that make up the pipe becomes a random coil shape or folded crystal that is favorable for entropy, and the molecular chains that support stress are about 1/1000 per cross-sectional area. It was a die molecular chain (molecular chain that connects folded crystals) and did not exhibit the original physical properties of plastic.

Therefore, it is possible to improve the physical properties by applying a stretching operation in the axial direction or circumferential direction of the pipe to orient the molecular chains in the stretching direction. This method is conventionally known for maintenance, film, etc.; however, for continuous stretching of pipe-shaped objects, thin-walled inflation forming is used, and thick-walled pipes are drawn using the drawing method that has been practically used for steel pipes, etc. are only partially introduced.

In these methods, either the unsolidified pipe extruded from an extrusion molding machine is stretched, or the pipe is completely cooled and solidified and then reheated from the outside surface of the pipe and stretched. The stretching effect could not be achieved, and the latter had the disadvantage that uniform stretching could not be achieved due to temperature differences in the thickness direction. Therefore, the problem when drawing thick-walled pipes is to control the temperature to the optimum temperature for pipe drawing, and the inventors of the present invention have conducted intensive research to make this possible, and have found that the drawing effect is uniform. This led to the development of a method to fully express this effect.

That is, in the present invention, after a pipe-like object is continuously extruded from an extrusion molding machine, the outer surface of the pipe-like object is rapidly cooled in a cooling liquid tank, and after the inner surface of the pipe reaches a temperature at which it can be stretched, the outer surface of the pipe-like object is It is an object of the present invention to provide a method for controlling the temperature of a pipe-shaped material, which can equalize the temperature in the thickness direction by heating the pipe again.

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a cross section of an apparatus showing an embodiment of the present invention for uniformizing the temperature in the thickness direction of an extruded pipe-like object, in which 1 is a pipe-like object, 2 is 3 is a cooling liquid tank, 3 is an infrared heater, 4 is a cooling liquid leakage prevention plate, and 5 is a sizer. FIG. 2 is a diagram schematically showing temperature changes on the inner and outer surfaces of the extruded pipe. Also, Figures 3 and 4
The figure shows an embodiment different from that in Figure 1, in which 6 is an electric or jacket heater, 7 is a heating liquid tank,
Reference numeral 8 is a dividing plate for the cooling liquid and heating liquid, and 9 is a heating liquid leakage prevention plate. Further, A indicates the direction in which the pipe moves.

The present invention can be applied to pipe-shaped articles made of thermoplastic polymer materials such as polyvinyl chloride, polyethylene, polypropylene, polyester, impact-resistant polystyrene, and acrylonitrile copolymers. I will explain about it.

Polyesters are polyethylene terephthalate and its homologous polymers, and polyesters obtained from terephthalic acid or ester-shaped derivatives and ethylene glycol or ester-shaped derivatives are used.

Now, polyethylene terephthalate chips with η = 1.0 and moisture content of 0.005% are melt-kneaded using an extrusion molding machine.
A pipe-like object 1 is extruded from a pipe die. The temperature of the pipe-like material is 285°C at the exit of the pipe die, and the viscosity of this resin is 25,000 poise. Polyester tends to undergo hydrolysis and thermal decomposition when heated and melted, so it cannot be heated to 270 to 300℃ above its melting point in an extruder.
It is desirable to mold in the temperature range of . The extruded pipe-like article 1 passes through a sizer 5 and is cooled in a cooling liquid tank 2.

The sizer 2 is preferably a vacuum sizer, but an extruded pipe does not necessarily require roundness, and other methods may be used as long as a pipe with a uniform thickness distribution can be extruded using a pipe die. In addition, the coolant in the coolant tank 2 is
Although water is generally used, a surfactant liquid may also be used to lubricate the sizer 5 and the dividing plate 4. Furthermore, after cooling, the cooling liquid is circulated through a pump and a cooler in order to equalize the temperature inside the cooling liquid tank 2 and increase the heat transfer coefficient with the pipe-like object. As shown in Fig. 2, the temperature of the pipe-like object in the cooling liquid tank 2 is such that the outer surface that comes into contact with the cooling liquid is cooled rapidly, and the inner surface is cooled later than the outer surface because it is cooled by heat conduction through the polyester. Ru.

The temperature range at which polyester can be stretched is 70 to 150°C, which is higher than the glass transition temperature, and preferably 80 to 120°C. Therefore, when the inner surface temperature of the pipe-shaped object 1 running in the cooling liquid tank 2 reaches 80 to 120°C, the pipe-like object 1 is caused to pass through the cooling liquid tank 2. The cooling process of the pipe-like object 1 is determined by the coolant tank inlet temperature of the pipe-like object 1, the wall thickness of the pipe-like object, the coolant temperature, and the flow state of the coolant (heat transfer coefficient). The cooling liquid temperature and cooling liquid flow condition become control factors. Next, the pipe-shaped object 1 that has passed through the cooling liquid tank 2 is heated from the outside by an infrared heater 3, and the temperature of the inside and outside surfaces is 90~90°C.
The temperature is controlled to 100°C and the next stretching process is started.

Example A polyester chip with η=1.0 and a moisture content of 0.005% was extruded into a pipe having an outer diameter of 20 mm and a wall thickness of 1 mm at a speed of 3 m/h using an extrusion molding machine. This extrudate had a cooling liquid bath inlet temperature of 285°C. Cooling water cooled to 5℃ was flowed into the cooling liquid tank 2 at a flow rate of 300 mm/sec, facing the pipe, and when the pipe was passed through the cooling liquid tank, the inner temperature of the pipe was 93℃ and the outer surface of the pipe was 93℃ after 11 seconds. The temperature reached 24℃. Next, when it was passed through a pipe-shaped infrared heater with an emissivity of 0.93 and a surface temperature of 470°C, the inner temperature of the pipe became 92°C and the temperature of the outer surface became 93°C after 2 seconds. This pipe became a drawn pipe that could be processed well in the next drawing process.

A similar effect was obtained by passing the pipe that had passed through the cooling liquid tank in the same manner as described above through the electric heating or jacket heater 6 shown in FIG. 3, the heating liquid tank 7 shown in FIG. 4, and further through the hot air tank. In addition, the heating zone of the pipe that has passed through the cooling liquid tank may be set up in the two-zone method of cooling liquid tank + heating of each method described above, or in addition, two or more zones may be installed using the same heating method or a mixed heating method. Heating time can be shortened by setting the heating temperature immediately after the liquid tank to a high temperature.

Furthermore, after passing through the cooling liquid tank 2, a method of removing the cooling liquid adhering to the surface of the pipe-shaped object using a liquid draining roll or gas blowing may be used in combination, and liquid draining and heating are performed at the same time. Therefore, it is also possible to spray heated gas.

As explained in detail above, the present invention involves continuously extruding a pipe-like object from an extrusion molding machine, then rapidly cooling the outer surface of the pipe-like object in a cooling liquid bath, and after the inner surface of the pipe reaches a temperature at which it can be stretched. Since the outer surface of the pipe-shaped object is reheated, the temperature in the wall thickness direction is made uniform, and the pipe is cooled once by a cooling body inside the pipe and then reheated, which was filed before the application of the present invention and published after the application was filed. There are no drawbacks such as the one shown in JP-A-55-121016, which has poor thermal efficiency and cannot obtain a stretched pipe with uniform physical properties because of the large temperature difference in the thickness direction.

[Brief explanation of drawings]

FIG. 1 is a side sectional view of a temperature control device that implements the method of the present invention, FIG. 2 is a diagram showing the relationship between the temperature control zone position and temperature, and FIGS. 3 and 4 are the same as FIG. 1, respectively. It is a side sectional view of a temperature control device showing a different example. Explanation of the main parts of the figure, 1...pipe-like object, 2...
...Cooling liquid tank, 3...Infrared heater, 5...Sizer, 6...Electric heating or jacket heater, 7...
...Heating liquid tank.

Claims (1)

[Claims] 1. When forming a plastic stretched pipe-like product, after continuously extruding the pipe-like product from an extrusion molding machine, the outer surface of the pipe-like product is rapidly cooled in a cooling liquid bath.
A method for controlling the temperature of a pipe-like object, which comprises heating the outer surface of the pipe-like object again after the inner surface of the pipe reaches a temperature at which it can be stretched.