JPS6228729B2 - - Google Patents

Description

[Detailed Description of the Invention] Pipes have a variety of uses, such as pipes for transporting materials and cans as containers, but demand for plastic pipes has been rapidly increasing recently for the purpose of corrosion resistance, weight reduction, etc. .

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. The plastic pipe formed in this way has a higher-order structure of the molecular chains that make up the plastic pipe, which has an entropically advantageous random coil shape or folded crystal.
The molecular chains that support the stress are tie molecules (molecular chains that connect folded crystals) that are about 1/1000 of the cross-sectional area, and the plastics did not exhibit their original physical properties.

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.
The method of improving the physical properties of plastic by stretching is a method that has been known for fibers, films, etc., but continuous stretching methods for pipe-like objects include thin-walled inflation molding, and thick-walled pipes such as steel pipes. Only some of the drawing methods that have been put into practical use have been introduced, and an industrial method for forming stretched pipes is not yet known.

If a method for producing stretched pipes of polyester, polypropylene, polyethylene, polyvinyl chloride, etc. in large quantities at low cost could be developed, can-shaped containers made from the above-mentioned plastic pipes could be obtained at low cost. Furthermore, among the plastics mentioned above, polyester is particularly desirable from the viewpoint of food hygiene, and since transparent containers can be obtained, it is possible to visualize the contents, which cannot be obtained with metal cans, etc., and is of great value in terms of distribution. The present inventors focused on this point, and as a result of intensive research to complete a continuous forming apparatus for polyester stretched pipes, they arrived at the present invention.

That is, the present invention provides an extrusion molding apparatus for extruding a stretched plastic pipe-shaped article, in which a stretched front part and a stretched part are continuously provided in the downstream part of the extrusion molding apparatus so that the inner diameter of the pipe-shaped article can communicate with each other. The stretching section forms a blow stretching machine whose inner and outer diameters are regulated by internal and external mandrels, and the stretching front section has a support rod of the internal mandrel as the center, and a space between the outer surface of the support rod and the inner surface of the pipe-shaped object. a gap is formed, and a part of the stretch blowing air sent through the support rod and blown into the stretching section is caused to flow in the opposite direction so as to be discharged from the extrusion molding device; and a plastic stretched pipe-like continuous forming apparatus in which stretch-blowing air is leaked from the internal mandrel, and a part of the stretch-blowing air is leaked between the outer surface of the support rod of the inner mandrel and the inner surface of the pipe-like object. By flowing the formed gap in the opposite direction so as to be discharged from the extrusion molding device,
It is an object of the present invention to provide an apparatus for continuously forming a pipe-like object, which can cool the pipe-like object and prevent it from sticking to an internal mandrel support rod.

An embodiment of the present invention will be explained below with reference to the drawings. Fig. 1 is a sectional view of a continuous stretch pipe forming apparatus showing an embodiment of the present invention, and Fig. 2 shows the draw ratio vs. stretch stress during stretch pipe forming. It is a line diagram.

In the figure, 1 is a pipe die, 2 is a sizer, 3 is an external mandrel, 4 is an internal mandrel, 5 is a fluid blowing hole, 6 is an internal mandrel support rod that also serves as a fluid transport pipe having the fluid blowing hole 5, and 7 is a fluid The exhaust hole 8 is a pipe-like member.

Polyesters include polyethylene terephthalate and its homologous polymers, and polyesters obtained from terephthalic acid or ester-forming derivatives and ethylene glycol or ester-forming derivatives can be used. Now, polyethylene terephthalate chips, which have been polyethylene terephthalate which have undergone intrinsic polymerization and have a moisture content of 0.005% and η=1.0, are melt-kneaded in an extrusion molding machine, and a pipe-shaped article 8 is extruded from a pipe die 1.

This pipe-like material 8 is required to be homogeneous because it will undergo a stretching operation in the subsequent process, and is kept at a temperature of 270°C to 310°C, which is higher than the melting point of polyethylene terephthalate, 265°C [measured by DSC (differential scanning calorimeter)]. Sufficient kneading is required in the area. The upper limit of the extrusion temperature is 310°C or higher, which is a dangerous range because polyethylene terephthalate tends to undergo thermal decomposition and hydrolysis when heated and melted, resulting in the production of acetaldehyde and deterioration of physical properties due to a decrease in molecular weight.

In addition, polyethylene terephthalate easily absorbs moisture, and the absorbed moisture promotes hydrolysis, so it is necessary to thoroughly dry the raw material chips and supply them to the extrusion molding machine with residual moisture of 0.01%, preferably 0.005% or less. In the embodiment shown in the drawings, a pipe-shaped article 8 was extruded at a temperature of 285° C. at the exit of the pipe die 1. The extruded pipe-like material 8 enters the sizer 2 and is cooled and solidified from the outside. Polyethylene terephthalate is a crystalline polymer, and when the melt is slowly cooled, spherulites are generated, which become cloudy and opaque and inhibit stretching. It must be cooled to pass.

The sizer 2 was of a cooling water bath type, and cooling water whose temperature was controlled at 25°C was circulated to rapidly cool the pipe-like object 8, and the pipe-shaped object 8 was passed through the sizer 2 so that the temperature reached 90°C. Polyethylene terephthalate is stretched at temperatures from 70°C to 150°C, preferably from 80°C to achieve its effect.
It is necessary to control the temperature to 120°C, and a temperature control device using hot air, infrared rays, a heating medium, an electric heating cylinder, etc. may be installed in the post-sizer 2 process.

Next, the behavior of blow-stretching will be explained according to Figure 2. Figure 2 shows the areal stretching ratio and stretching stress when blow-stretching a polyester pipe with an outer diameter of 20 mm and a wall thickness of 2 mm at 90°C. The broken lines in the figure indicate the blowing pressure during pipe stretching of 1, 2, 3,
This figure shows the change in force acting in the circumferential direction of the pipe as the pipe diameter increases due to stretching at a setting of 4 Kg/cm ² . As can be seen from the figure, polyester pipe requires a pressure of 3 kg/cm ² at a stretching ratio of 2 to 3 times, but the pressure required for stretching decreases further up to 5 times, and becomes less than 2 kg/cm ² at a stretching ratio of 5 times. Become. This tendency remains the same even if the pipe diameter, wall thickness, and temperature change.

As shown in FIG. 1, the blow molding machine has an external mandrel 3 and an internal mandrel 4 in the stretching section, and an internal mandrel support rod 6 that also serves as a fluid transport pipe having fluid blow holes 5 in the stretching front section. . The pipe-shaped article 8 whose temperature has been adjusted to the appropriate stretching temperature is stretched under pressure in a blow molding machine using a fluid having a pressure that allows stretching from the fluid blowing hole 5 located inside the pipe-shaped article 8. At this time, under stretchable pressure,
It is not possible to arbitrarily regulate the pipe diameter. There is an external mandrel 3 to regulate this.

The function of the external mandrel 3 is a separate pipe-like member 8.
Provides protection in case of rupture. Fluid injection hole 5
The blown fluid is supplied from the pipe die 1 etc. through a fluid transport pipe. After the pipe is stretched, this fluid is supplied to the pipe die 1 between the inner surface of the pipe-like object 8 and the internal mandrel 4, and between the pipe-like object 8 in front of the forming process and the outer surface of the inner mandrel support rod 6 which also serves as a fluid transport pipe. The fluid is discharged out of the system through the fluid discharge port 7.

However, since it is necessary to maintain the stretching pressure of the pipe-like material 8, it is desirable that the amount of leakage on the internal mandrel 4 side be small. Further, the discharge from the fluid discharge hole 7 side is actively carried out in order to cool the inner surface of the pipe-like object 8 extruded from the pipe die 1 and to prevent it from sticking to the internal mandrel support rod 6 which also serves as a fluid transport pipe. At this time, in order to prevent pressure from being generated during the discharge process, it is possible to use a pump or the like to exhaust the fluid from the fluid discharge hole 7, and to provide a constriction part with a larger diameter on the support rod 6 located at the small diameter part 3a of the external mandrel 3. desirable. Note that although the fluid blowing hole 5 has been described as an example provided in the support rod 6, the internal mandrel 4
The hole shape may be a plurality of round holes, elongated holes, etc., or these holes may be provided on both the support rod 6 and the internal mandrel 4. Pressurized air, pressurized nitrogen, etc. can be used as the blowing fluid.

As explained in detail above, the present invention involves stretching in a blow stretching machine whose outer diameter and inner diameter are regulated, and at the same time stretching the support rod in the gap formed between the outer surface of the support rod of the internal mandrel and the inner surface of the pipe-like object. A part of the stretch-blowing air sent through the inside and blown into the stretching section is made to flow in the opposite direction so as to be discharged from the extrusion molding device, and the stretch-blowing air is leaked from the front mandrel. By cooling the inner surface of the pipe-like object, it is possible to reduce the frictional resistance with the internal mandrel support rod that also serves as a fluid transport pipe, and the frictional part between the pipe-like object and the internal mandrel is only one place, allowing high speed Stretching can be done stably at low cost.

By the way, if a pipe-shaped object comes into contact with the internal mandrel support rod, especially in the part (high temperature part) near the pipe die (extrusion molding equipment), it may stick to the support rod or
The contact area may be locally cooled, making the next blowing process impossible. In the present invention, a part of the air for stretch blowing is made to flow in the opposite direction so as to be discharged from the extrusion molding apparatus, so that an air layer is created between the pipe-shaped article and the mandrel support rod to prevent contact between the two. This can be prevented and the problems mentioned above can be eliminated.

Furthermore, cooling of the pipe-like object is sufficiently effective even if the flow rate of the blown air is small. In other words, the pipe-like object does not need to be completely cooled in the entire thickness direction; just by creating a cooled skin layer on the inner surface of the pipe-like object, the coefficient of friction on the inner surface decreases rapidly, even if the pipe-like object is supported. Even if it comes into contact with the rod, its stickiness will not make it impossible to form. This is particularly important when molding polyethylene terephthalate, etc., whose friction coefficient does not reach 1 or less unless the temperature is about 80°C or lower.
In addition, the external surface of the pipe-shaped object before stretching (unstretched) is uniformly (all around) the sizer cooled by water cooling, etc.
Since the frictional resistance is cooled by contacting the surface, the frictional resistance inevitably decreases.

Furthermore, the resin extruded from the pipe die of the extrusion molding device enters the sizer in a high temperature state and has very low strength. On the other hand, the temperature in the stretching blow section is low and the strength is high, and the blowing air for stretching requires high pressure. Therefore, when this high blow pressure is applied from the extrusion molding apparatus side, the resin at the die outlet is swollen and destroyed by the air pressure, as shown in FIG. On the other hand, when the stretch blowing air is made to flow backwards as in the present invention, it is possible to provide a large air vent hole A in the die part of the extrusion molding apparatus, as shown in FIG. The internal pressure of the pipe-like article at the outlet can be made as low as is commensurate with its strength. In addition, if there is a need to reduce the pressure, suction can be performed using a vacuum device. Therefore, in the present invention, the pipe-like object is not destroyed as shown in FIG. 3 above.

[Brief explanation of the drawing]

FIG. 1 is a side sectional view of a continuous pipe forming apparatus showing an embodiment of the present invention, FIG. 2 is a diagram showing the relationship between the stretching ratio and stretching stress during the same stretched pipe forming, and FIGS. FIG. 4 is a sectional view for explaining the effects of the present invention. Explanation of the main parts of the diagram, 1... Pipe die (extrusion molding device), 2... Sizer, 3... External mandrel (blow stretching machine), 4... Internal mandrel (blow stretching machine), 5... Fluid blowing hole , 6... Internal mandrel support rod (blow stretching machine), 8... Pipe-shaped object.

Claims (1)

[Claims] 1. In an extrusion molding device for extruding a stretched plastic pipe-shaped article, a stretched front portion and a stretched portion are provided in succession at the downstream portion of the extrusion molding device so that the inner diameter of the pipe-shaped article can communicate with each other, and the stretched portion is and an external mandrel to form a blow stretching machine in which the inner and outer diameters are regulated, and the stretching front part has a support rod of the inner mandrel as the center, and a gap is formed between the outer surface of the support rod and the inner surface of the pipe-shaped object. A part of the stretch blowing air sent through the support rod and blown into the stretching section is caused to flow in the opposite direction through the same gap so as to be discharged from the extrusion molding device, and 1. An apparatus for continuously forming a plastic stretched pipe-like article, characterized in that air for stretching and blowing is leaked from the pipe.