JPH0622874B2 - Heating method for polymer resin moldings - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for heating a thermoplastic bottle or a preform, and more particularly to a thermoplastic preform having a bottomed cylindrical body and mouth. A method of uniformly heating the body of the preform in the production of a bottle by blow molding, and crystallizing the mouth of the thermoplastic bottle or preform to obtain dimensional stability at high temperatures. Heating method for heating.

[Conventional technology]

When the contents of a thermoplastic bottle are filled at a high temperature, the mouth is heated and deformed by heat, so that the lid cannot be sealed.

Therefore, thermal deformation is generally prevented by crystallizing the mouth of a plastic bottle. As a method therefor, conventionally, a method of covering a mouth with a cap and heating the cap by an induction heating method (JP-A-55-55)
12031) A method in which a heating cover is arranged around the mouth and hot air is blown into the heating cover (Japanese Patent Laid-Open No. 61-79627).
Alternatively, a method of arranging electrodes inside and outside the mouth and applying a high frequency voltage to the electrodes to heat them by high frequency induction (Japanese Patent Laid-Open No. 58-2
17326) and the like are known.

Further, when a bottle is manufactured by blow molding from a thermoplastic preform consisting of a bottomed cylindrical body and a mouth, it is necessary to heat the body of the preform. An infrared heater was placed outside the to heat the preform from the outside.

[Problems to be solved by the invention]

Infrared heater of the plastic bottle by covering the mouth of the plastic bottle with a cap and inductively heating it, by arranging a heating cover around the mouth and blowing hot air into the heating cover, or by preforming the preform from the outside. In any of the heating methods, the body of the preform and the mouth of the plastic bottle are heated from the outside, and the heat is transferred from the outside to the inside of the plastic resin tube wall. In this case, the thermal conductivity of the plastic resin is low, and it takes a long time to sufficiently move up and down inside. Further, in order to rapidly raise the temperature of the inside to a desired temperature, the temperature of the outer surface must be raised, and the outside becomes overheated, which deteriorates the properties of the material. Furthermore, it is difficult to obtain a uniform temperature distribution inside and outside.

On the other hand, in the method of heating by the dielectric heating method, the heating rate of each part is determined by the shape of the electrode and the object to be heated, but it is difficult to make it uniform, and the part where the temperature locally rises due to heating It is difficult to perform uniform heating because the heating rate further increases and the temperature rises extremely.

The present invention has been made to solve the above problems, and an object thereof is to provide a method for uniformly heating a thermoplastic bottle or preform in a short time.

[Means for solving problems]

Microwaves are introduced into the cavity resonator, and the high electric field region and low electric field region of the standing wave existing in the cavity resonator in resonance are repeated while rotating the heated portion of the polymer resin molded product. The polymer resin molded product is heated by passing it. Even more uniform heating can be achieved by concentrating and heating infrared rays at a specific place while rotating the object to be heated before or after the heating by the micro standing wave.

[Work]

When a standing wave in a resonant state is created in the cavity resonator and the polymer resin molded product is passed through while rotating in the high electric field region and the constant electric field region, the polymer resin molded product is heated. It is heated strongly at times and weakly at other times.
According to such a heating method, so-called thermal runaway in which a portion of the object to be heated is heated strongly and the portion is heated more and more is hindered. Further, by irradiating the object to be heated with the collected infrared rays, the temperature distribution of the object to be heated can be effectively controlled. That is, if the portion of the object to be heated which is desired to be strongly heated is previously irradiated with infrared rays, the temperature of the portion is increased and the microwave heating is facilitated. On the contrary, the temperature distribution can also be controlled by heating the object to be heated by microwaves and then irradiating the part of the object to be heated with infrared rays.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings. As shown in FIG. 1, the mandrels 3, 3 ... Supporting the preform 1 circulate between the respective rotary tables in the order shown by the arrows. That is, the preform delivery table 4 to the transfer table 5, the heating station table 6, the annealing station tables 7 and 8, the transfer table 9, the blow molding station table 10, and the transfer table 1.
The preform delivery table 4 and the hemandrels 3, 3 ... Are circulated again with a diameter of 1, but the mandrel holding mechanism and delivery mechanism in each table are not shown because they are performed by a conventionally known method. On the mandrels 3, 3 ...
Preforms 1, 1 ... Are attached with diameters 2, 13. The preform 1 has a cross-sectional shape shown in FIG. 2 and has a cylindrical body portion 15 having a bottom and a mouth portion 16 having a thread and an annular protrusion.
Is made up of. While the preform 1 is attached to the mandrel 3 and circulates in the normal path, the body is heated by the heating station table 6 and blow molded by a conventionally known method at the blow molding station table. Bottle 2 is manufactured. The manufactured thermoplastic bottle 2 is taken out from the mandrel 3 held on the delivery table 4 by a conventionally known device and sent out through the delivery table 14 in diameter. The mandrel 3 has a sectional shape shown in FIG. 4, and is integrally provided with circumferential grooves 17 and 17 for holding it on each table and sprockets 18 and 18 for rotationally driving. Chains are stretched around the heating station table 6 and the annealing station tables 7 and 8 through which the mandrels 3 and 3 pass in order to form a staircase, and mesh with the upper and lower sprockets 18 and 18 to rotate the mandrel. Driven to give. However, the chain is not shown.

Next, the apparatus attached to the heating station table 6 and the heating operation will be described with reference to FIGS. 2 to 7. Mandrel holding devices 19 are attached to the heating station table 6 at equal intervals, and arc-shaped cavity resonators 20 are provided along the periphery of the table. As shown in FIG. 5, the polyfoam 1 inserted in the mandrel is rotatably conveyed in the cavity resonator 20. In order to prevent radio wave leakage, the both ends of the cavity resonator 20 have a rectangular cross section with a length equal to or longer than one wavelength of the standing wave existing in the cavity resonator as shown in FIG. The cutoff wavelength of the cross section is smaller than the wavelength of the standing wave existing in the cavity resonator. Lower surface of resonator 2
1 has a slit so that the preform 1 can pass through it, but it advances while rotating so that the ring-shaped brim 22 attached to the upper part of the mandrel is pressed against the lower surface of the resonator in order to prevent radio wave leakage from the lower surface. It is a mechanism to do. At this time, a thin Teflon sheet 23 is provided between the lower surface of the resonator and the ring-shaped brim so as not to cause discharge. Further, a protrusion such as a post 27 may be provided inside the cavity resonator 20 so that the electric field can be controlled. The preform 1 is dielectrically heated by alternately passing the strong and weak electric fields of the standing wave generated in the resonator, but each part of the preform immediately shifts to the weak electric field after passing the strong electric field. The phenomenon of thermal runaway seen when a so-called uniform electric field is applied does not occur. An infrared heating zone composed of a heating unit 26 as shown in FIG. 7 is provided to correct the temperature unevenness of the preform. When this infrared heating zone is provided in the preceding step of the dielectric heating zone, the infrared-heated portion is more likely to be heated in the next dielectric heating zone, and when provided in the subsequent step, the heating that is insufficient in the dielectric heating The portion can be corrected, and in either case, a desired temperature distribution can be obtained. The heating unit 26 is composed of an infrared heater 24 and a reflecting mirror 25, and irradiates infrared rays toward the preform 1 which rotates together with the mandrel 3. The reflecting mirror 25 has an elliptical surface and is attached so that infrared rays can be focused on a portion where heating is insufficient due to dielectric heating. The preforms heated on the preform heating station table 6 in this way are processed by the annealing stations 7 and 8.
And is blow-molded into a bottle at the blow molding station 10. FIG. 8 is a cross-sectional view showing another embodiment of the present invention, in which the mouth of the preform is crystallized. The preform is supported with its mouth facing upward, and is subjected to a rotation motion to be dielectrically heated in the cavity resonator. Posts 27 are erected in the cavity resonator 20, and the electric field can be controlled by the shape and insertion depth of the posts. A part of the heating unit for heating the outside of the preform in the embodiment shown in FIG. 1 is replaced by the infrared condensing device 26 'shown in FIG. The infrared condensing device 26 'is composed of a reflecting mirror 25' having an elliptical cross section and a linear infrared heater 24 '.
The radiant heat from the infrared heater arranged at one focus of 5'is concentrated on the protruding portion of the mouth portion of the preform arranged at the other focus. In this way, the entire mouth of the preform is heated to the required temperature.

〔The invention's effect〕

As described above, since the mouth portion of the thermoplastic bottle or the preform or the body portion of the preform is heated from the inside and the outside, the time required for heating is shortened and the productivity is improved. Further, it becomes possible to uniformly heat each part.

[Brief description of drawings]

FIG. 1 is a plan view schematically showing an embodiment of the present invention, FIG. 2 is a sectional view of a preform 1 heated in this embodiment,
3 is a sectional view of a thermoplastic bottle manufactured by blow molding from the preform 1, FIG. 4 is a sectional view of a mandrel 3 supporting the preform 1, and FIG. 5 is a sectional view taken along line AA in FIG. 6 and 6 are schematic views showing the loading / unloading end of the cavity resonator, FIG. 7 is a sectional view taken along line BB in FIG. 1, and FIG. 8 is a perspective view showing another embodiment of the present invention. FIG. 9 is a sectional view showing an infrared heating unit in another embodiment of the present invention. 1 ... Preform, 2 ... Thermoplastic bottle, 3 ... Mandrel, 4 ... Delivery table, 5,
9, 11 ... Transfer table, 6 ... Heating station table, 7, 8 ... Annealing station table, 10 ... Blow molding station table, 12,
13 ... Supply table, 14 ... Sending table, 15 ...
… Body part, 16 …… Mouth part, 17 …… Surround groove, 18 …… Sprocket, 19 …… Holding device, 20 …… Cavity resonator, 21
...... Resonator bottom surface, 22 ...... Ring-shaped brim, 23 ...... Insulation sheet, 24 ...... Infrared heater, 25 ...... Reflector, 26 ...
… Heating unit, 27 …… Post.

Claims (3)

[Claims] 1. A high temperature region and a low electric field region of a standing wave existing in a resonance state in the cavity resonator when a microwave is introduced into the cavity resonator, and a portion to be heated of a polymer resin molded article. A method for heating a polymer resin molded article, characterized in that the resin is repeatedly passed while rotating. 2. A high electric field region of a microwave standing wave existing in a resonant state in a cavity resonator, where infrared rays are condensed and heated in advance at a specific portion of a heated portion of a polymer resin molded article, and A method for heating a polymer resin molded article, which comprises repeatedly passing a low electric field region while rotating the entire portion to be heated. 3. A high electric field region and a low electric field region of a microwave standing wave existing in a resonance state in a cavity resonator are repeatedly passed while rotating a heated portion of a polymer resin molded product, and then the aforementioned object A method for heating a polymer resin molded article, characterized in that infrared rays are focused on a low heating portion of a heating portion and heating is performed while additionally rotating.