JPS631173B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method and apparatus for producing a molecularly oriented plastic molded article by stretch molding, and more specifically, to a method and apparatus for producing a molecularly oriented plastic molded article by stretch molding. The present invention relates to a method and apparatus for producing a molecularly oriented plastic molded body, which enables thermal fixation of the plastic molded body or accurate profile formation by cooling the mold temperature.

It has been noticed that molecular orientation through stretch molding improves various properties of plastic molded products such as strength, gas barrier properties, and transparency, and recently stretch molded plastic molded products such as polyethylene terephthalate bottles and polypropylene bolts have It is starting to be put into practical use. These bottles are manufactured by biaxial stretch blow molding,
At this time, the mold surface temperature is usually kept below room temperature. This is to prevent whitening of the molded product and deformation of the molded product when taken out from the mold by rapidly cooling the molded product. Polyethylene terephthalate bottles and the like manufactured in this manner have satisfactory performance for use in carbonated beverages, soy sauce, cosmetics, etc., which do not require heat sterilization after filling with contents. But about 70
When heated above 0.degree. C., unsightly deformation occurs due to residual strain, so there is a problem that it is not suitable for filling and sealing contents that require heat sterilization, such as youth products. Several proposals have been made in the past regarding methods of preventing thermal deformation of such stretched plastic products, ie, heat setting methods. For example, JP-A-54
- No. 77672 states that during stretch molding, the mold is heated to a high temperature, and after heat-setting, a cooling liquid is passed through the mold to obtain the temperature of the molded product to the extent that the molded product will not be deformed by external force. A method has been proposed in which the molded product is taken out after being lowered to a certain point. However, since the cooling rate of the mold is slow in this method, there is a problem in that productivity is significantly lower than in the conventional simple stretch molding method. Furthermore, in JP-A-53-78267, after stretch-blow molding a hollow body, the pressure inside the mold is reduced before opening the mold, the hollow molded body is brought into close contact with the mold, and heated gas is introduced into the inside of the hollow body. A method has been proposed in which the hollow body is heat-set by blowing and then cooled by blowing in room-temperature compressed gas, but this method also has the problem of increasing the number of steps and having poor productivity.
Furthermore, in Japanese Patent Application Laid-Open No. 54-66968, a stretch-molded bottle is enclosed in another mold, the mold is heated with high-pressure gas filled, and the mold is heat-set. A method of cooling a mold is disclosed. In this case as well, there are problems in that two types of molds must be prepared, the number of steps increases, and productivity is poor.

The present invention has been made in view of the above-mentioned prior art, and the main object of the present invention is to provide a method and apparatus for stretch-molding thermoplastic plastics that are capable of rapidly heating and cooling a mold. There is a particular thing. A particular object of the present invention is to provide a highly productive method and apparatus for manufacturing heat-set, molecularly oriented saturated polyester resin containers.

In order to achieve the above object, the present invention provides a method for producing a molecularly oriented plastic molded article by stretch-molding a thermoplastic heated to a stretch-molding temperature within a mold cavity. After introducing a liquid into the cavity provided inside and sealing it, the liquid is heated to raise the cavity surface of the mold to approximately the above-mentioned stretch-molding temperature, thereby raising the temperature of the stretch-molded plastic molded article. contacting the raised cavity surface, and before removing the plastic molded body from the mold, releasing the seal to vaporize the liquid and cooling the cavity surface to a temperature approximately lower than the stretch molding temperature; A method for manufacturing a molecularly oriented plastic molded body, and an apparatus for manufacturing a molecularly oriented plastic molded body by stretching and molding a thermoplastic plastic heated to a stretching temperature in a cavity of a mold, characterized by: A mold having a cavity disposed therein surrounding a surface, a means for heating a liquid sealed in the cavity, a first conduit for introducing the liquid into the cavity, and a first conduit for introducing the liquid into the cavity. A first on-off valve attached to a conduit, a second on-off valve for sending vaporized vapor of the liquid from the cavity, a second on-off valve attached to the second conduit, and for liquefying the vapor. After the liquid is introduced into the cavity, the first on-off valve and the second on-off valve are closed to seal the liquid in the cavity, and after the end of the stretch forming, the liquid is introduced into the cavity. The present invention provides an apparatus for producing a molecularly oriented plastic molded article, characterized in that it is equipped with an on-off valve control device for opening the on-off valve and sending out the vaporized vapor of the liquid through a second conduit.

The present invention will be explained below.

The thermoplastics to which the present invention is applied may be those having molecular orientation, and examples of such oriented thermoplastics include cotton-like saturated polyester resins such as polyethylene terephthalate, polytetramethylene terephthalate,
Examples of polyolefin resins include polypropylene, polyethylene, polycarbonate resins, nitrile resins, copolymers and blends containing these as main components, and laminates containing oriented thermoplastics of these as main layers.

Hereinafter, an example of heat setting of a stretch-molded polyethylene terephthalate bottle will be described with reference to a drawing which is an example.

In Figure 1, a bottomed parison (not shown) heated to a stretch blowing temperature (approximately 80 to 100 degrees Celsius) is placed inside a split mold 1 (made of an aluminum alloy with good thermal conductivity) using a stretching rod. 2 shows a state in which the bottle 3 is stretch-blow molded and the outer surface 3a of the bottle is in close contact with the cavity surface 1a of the mold 1. A cavity 1b is provided inside the mold 1 so as to surround the cavity surface 1a. The cavity 1b serves as a medium for heating and cooling the cavity surface 1a. a conduit 5 (FIG. 2) for introducing the liquid 4;
and a conduit 6 for delivering vaporized vapor of the liquid 4
(Figure 2) are connected. Further, a heating coil 7 is disposed inside the cavity 1b, and the liquid 4 is heated by the heating medium circulating inside the heating coil 7 to approximately the stretching blow temperature, which is a temperature higher than the boiling point of the liquid 4. It is configured.

In FIG. 2, 8 is a liquid tank, and 9 is a liquid tank 4.
10 is a pump for supplying liquid 4 to the mold 1.
This is a heater for preheating water to a temperature close to its boiling point. 11 and 12 are on-off valves, 13 is a relief valve, and 14 is a cooler for cooling and liquefying the vaporized liquid 4 heated above the boiling point in the mold 1. 15 is a heater for heating the heating medium (water, oil, etc.) flowing back through the heating coil 7, 16 is a pump, and 17 is an on-off valve. 18 is an on-off valve 11,1
This is an on-off valve control device for opening and closing 2 and 17 at predetermined timing. Opening/closing valve control device 18
As shown in the timing chart of FIG. 3, when the mold 1 opens, the on-off valve 11 is opened and the liquid 4 is released.
is introduced into the cavity 1b, and when the mold 1 closes, the on-off valves 11 and 12 are closed to seal the liquid 4 in the cavity 1b, and at the same time, the on-off valve 17 is opened to close the heating coil 7.
By supplying a heating medium into the tank to heat the liquid 4 to approximately the stretching blow temperature, which is a temperature higher than its boiling point, and then simultaneously opening the on-off valve 12 and closing the on-off valve 17, the liquid 4 is rapidly vaporized. After lowering the cavity surface temperature, the opening/closing valve 11 is opened at the same time as the mold 1 is opened.

Heat setting of the stretched blow bottle is carried out in the following manner using the above-described apparatus.

First, the mold 1 is opened in order to remove the bottle molded in the previous step and insert a new bottomed parison into the mold. At the same time, the on-off valve 11, which had been closed until now, opens and the temperature is slightly lower than the boiling point (for example, 60°C).
℃) is introduced into the cavity 1b (at this time, the on-off valve 12 is also open).
Although it is preferable that the liquid 4 fills the cavity 1b,
It does not necessarily have to be full. Since the preferred stretch-blowing temperature of the polyethylene terephthalate parison is about 80 to 100°C, the liquid 4 used in this case is preferably methyl alcohol, ethyl alcohol, or a mixture thereof. The boiling point of methyl alcohol (1 atm) is 64.7°C and its latent heat of vaporization is 264 cal/g, and the boiling point of ethyl alcohol (1 atm) is 78.3°C and its latent heat of vaporization is
205 cal/g, the boiling point of each is slightly lower than the stretch blowing temperature, and the latent heat of vaporization is large, so the cooling ability by vaporization is high. At the same time as the bottle molded in the previous step is removed from the mold 1, the on-off valves 11 and 12 are closed, and the on-off valve 17 is closed.
By opening, the liquid 4 sealed in the cavity 1b is heated, and the cavity surface temperature is heated to a temperature close to the stretch blow temperature, for example, 90° C., as shown in FIG. 3f. This temperature is the relief valve 13
It is determined by the set pressure of , and can be controlled at a constant level. On the other hand, after the bottle has been taken out, the parison is loaded, and at the same time as the loading is finished, the mold 1 is closed, and at the same time, the stretch rod is pushed down and compressed air is blown in to perform stretch blow molding. Figure 3 a, b). Since the air blowing is continued until the start of taking out the bottle, the outer surface of the molded bottle 3 and the heated cavity surface 1a are in close contact for a sufficient period of time and heat-fixed. At this time, the liquid 4 is heated above its boiling point, so its pressure increases, and the pressure and temperature are set by the relief valve 13. Next, while the mold 1 is closed, the on-off valve 12 is opened, and the on-off valve 17 is closed (Fig. 3 d, e), and the superheated liquid 4 is rapidly vaporized, absorbing heat from the mold 1 and exposing the cavity surface 1a. Cool to a temperature below the second order transition temperature of polyethylene terephthalate, preferably about 40-70°C. Therefore, the bottle 3 is also cooled in a very short time to a temperature at which no deformation occurs during removal. After that, the mold 1 is opened and the bottle 3 is taken out. This one step can be completed in a short time of about 20 seconds. Therefore, even if a heated mold is used during stretch blow molding, there is no risk of whitening of the bottle product.

In the above embodiment, the on-off valve 17 was turned on and off, but the on-off valve 17 may be left open. Further, it is preferable that the cavity surface reaches approximately the above-mentioned stretch-blow temperature at the end of stretch-blow molding, but it does not necessarily have to reach this temperature. Further, in the above embodiments, the liquid 4 was heated by a liquid medium, but any other heating means such as electric heating, burner heating, etc. may be used. However, heating with a liquid medium, particularly hot water, has the advantage that it is safer since there is no risk of ignition, and that more uniform heating is possible.

Although the case where polyethylene terephthalate is used as the thermoplastic resin has been described above, the present invention can also be applied to polypropylene bottles. However, the stretching blow temperature in this case is approximately 160℃
Therefore, there is no need to perform heat fixation. However, by raising the cavity surface to approximately 180℃ during molding,
Then, by rapidly cooling to about 100℃,
Since the thread profile of the bottle neck can be sharp, it is possible to solve the problem of not being able to obtain an accurate thread profile when using a conventional cooled mold. Furthermore, it goes without saying that the present invention can be applied to the stretch molding of cup-shaped hollow bodies or containers by plug-assisted stretch molding or the method previously proposed by the present inventor in Japanese Patent Application No. 54-99480.

According to the present invention, the mold cavity surface can be cooled extremely rapidly by utilizing the latent heat of vaporization of the liquid. Thermoplastics can be stretch-molded at almost the same high production rate as when using a cooling mold. Furthermore, since the temperature can be controlled using pressure, there is no need for a conventional temperature regulator, and the mold temperature is much more uniform than other methods. Therefore, it is possible to add a heat-setting process to the conventional stretch-blowing process without reducing its productivity, so that molecularly oriented containers made of saturated polyester resin that can be heat sterilized without whitening can be produced at high speed, for example, by It has the advantage of being able to be manufactured in a ~30 second cycle.

A specific example will be explained below.

The mold with the structure shown in Figure 1 (made of aluminum alloy, the thickness between the cavity surface and the cavity is 10 to 15 mm)
mm), take out the bottle molded and heat-fixed in the previous process, and open the on-off valve 11 at the same time as opening the mold.
I opened it. At this time, the on-off valve 12 is open. In this specific example, the on-off valve 17 was kept open at all times. At the same time as opening the on-off valve 11, a mixture of 50% by weight methyl alcohol and 50% by weight ethyl alcohol at a temperature of 60°C (boiling point approx.
70℃) flows back, and the mold cavity surface temperature drops to 60℃. Simultaneously with the completion of taking out the bottle from the mold, the on-off valves 11 and 12 were closed, and the alcohol mixture was heated by the heating coil 7 in a sealed state. Due to this heating, when the mold cavity surface temperature rose to approximately 80℃, a polyethylene terephthalate bottomed parison (injection molded product) with an outer diameter of 30mm, a body wall thickness of 2.5mm, and a length of 150mm was heated to 95℃. is charged into the mold, the mold is immediately closed, the stretching rod 2 is pushed down, compressed air (20 kg/cm ² ) is forced into the parison through the guide hole 2 provided in the stretching rod 2, and the parison is stretched. Blow molding was performed. In order to heat-fix the molded bottle, compressed air is held inside the bottle until the mold is opened even after stretch blow molding, and the molded bottle is heated to a temperature of 90°C at the end of the molding process. tried to maintain contact. The outside diameter of the body of the molded bottle is 80mm, and the average wall thickness of the body is
0.3mm, and the total height was 255mm. Opening/closing valves 11, 12
10 seconds after closing, the on-off valve 12 was opened to cool the mold. Five seconds after opening the on-off valve 12, when the cavity surface had cooled to 70°C, the mold was opened, the bottle was taken out, and the following operations were repeated. The temperature of the cavity surface was measured at the center of the body using Thermopyure (trade name, radiation thermometer).

The bottle could be taken out without being deformed, and there was no whitening phenomenon. 80℃ in this bottle
The chamber was filled with warm water and sealed, and the change in internal volume before and after was measured. The change in internal volume was extremely small, a decrease of 0.3% compared to before filling with hot water, and no thermal deformation such as dents was observed even by visual observation.

[Brief explanation of the drawing]

Fig. 1 is a longitudinal cross-sectional view of one embodiment of a mold used in the present invention, Fig. 2 is a piping diagram of an apparatus which is an embodiment of the present invention, and Fig. 3 is a diagram showing the method of carrying out the method of the present invention. This is an example of a timing chart. DESCRIPTION OF SYMBOLS 1... Mold, 1a... Cavity surface, 1b... Cavity part, 3... Bottle (molecularly oriented plastic molded object),
4...liquid, 5...first conduit, 6...second conduit, 7
... heating coil (means for heating liquid), 11... first on-off valve, 12... second on-off valve, 14... cooler (cooling device), 18... on-off valve control device.

Claims (1)

[Scope of Claims] 1. In a method for manufacturing a molecularly oriented plastic molded article by stretching and molding a thermoplastic plastic heated to a stretching temperature within a cavity of a mold, After introducing a liquid into the molded cavity and sealing it, the liquid is heated to raise the cavity surface of the mold to approximately the above-mentioned stretch-molding temperature, and the stretch-molded plastic molded body is heated to the heated temperature. The liquid is brought into contact with the cavity surface, and before the plastic molded body is removed from the mold, the seal is released to vaporize the liquid, and the cavity surface is cooled to a temperature approximately lower than the stretch molding temperature. A method for producing a molecularly oriented plastic molded article. 2. The method for producing a molecularly oriented plastic molded article according to claim 1, wherein the stretch molding is stretch blow molding. 3. The method for producing a molecularly oriented plastic molded article according to claim 2, wherein the thermoplastic plastic is polyethylene terephthalate. 4. The method for producing a molecularly oriented plastic molded article according to claim 3, wherein the stretching temperature is about 80 to 100°C. 5. The method for producing a molecularly oriented plastic molded article according to claim 3, wherein the liquid is methyl alcohol, ethyl alcohol, or a mixture thereof. 6. The method for producing a molecularly oriented plastic molded article according to claim 3, wherein the molecularly oriented plastic molded article is a heat-set molded article. 7. In an apparatus for manufacturing a molecularly oriented plastic molded article by stretching and molding thermoplastic plastic heated to a stretching temperature within a cavity of a mold, a cavity surrounded by a surface of the cavity and a A mold having a means for heating a liquid sealed in a cavity, a first conduit for introducing the liquid into the cavity, a first on-off valve attached to the first conduit, and the cavity. a second conduit for sending out the vaporized vapor of the liquid, a second on-off valve attached to the second conduit, and a cooling device for liquefying the vapor;
After the liquid is introduced into the cavity before stretch forming, the first on-off valve and the second on-off valve are closed to seal the liquid in the cavity, and after the end of stretch forming, the second on-off valve is closed. 1. An apparatus for producing a molecularly oriented plastic molded article, comprising an on-off valve control device for opening and sending vaporized vapor of the liquid through a second conduit.