JPH09104067A - Method for curling mouth part of synthetic resin container and local heater used therein - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a processing method locally heating a region to be curled to bend and curl the mouth flange part of a container downwardly or inwardly, a method for curling the mouth part of a safe synthetic resin container not injuring a lip by a mouth part and ensuring the max printing area on the side surface of the container and to provide a local heater used in those method. SOLUTION: In a synthetic resin container consisting of a container main body 11 and the opening flange 14 extending from the outer periphery of the opening part 12 of the container main body and having a mouth part formed by the curl processing of the opening flange, the rear surface of the opening flange is locally heated by a local heater 30 and, thereafter, the opening flange is subjected to curl processing.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for curling the mouth of a synthetic resin container that can be used as tableware for food packaging or when eating contents, and a local heating device used therefor, and more specifically to the opening of the container body. TECHNICAL FIELD The present invention relates to a curling method and a local heating device for locally heating an opening collar projecting on the outer periphery of a portion and curling it to form a safe mouth portion having a good mouth feel.

[0002]

2. Description of the Related Art A sheet-shaped raw material such as a non-foamed resin container (hereinafter referred to as "solid container") or a foamed resin sheet container is heated and then sandwiched by male and female molds to open the container body. A synthetic resin container adopts a molding process in which the opening flange is integrally projected on the outer periphery of the part, and then the molded product is cut off from the sheet with a punching blade. And sharp edges are created.
This sharp edge has a high risk of injury, especially in a food container or the like that is brought into contact with soft skin or lips and used for eating, and is regarded as dangerous in the market. Further, industrially, when a shrink film or the like is used for the exterior, there is a problem that the shrink film is broken due to a sharp edge.

Further, it is said that it is preferable in view of the container design that the size of this flange portion is as small as possible.
In addition, the mouthfeel is improved. However, the mouth collar has a deep relationship with the compressive strength in the direction of squeezing the container, such as the force when applying the shrink film, and in reality it is desirable to make it as large as possible in terms of strength. I can't.

In order to solve this problem, a so-called curl treatment has been proposed in which an opening flange formed in advance on the outer periphery of the opening of the container body with a margin for curling is folded downward. For this curl treatment, a curl device manufactured by Brown Co. of the United States of America is proposed and manufactured.

An outline of the curl device will be described by taking the device of Brown Co. as an example. As shown in FIGS. 4 to 7, the curl device 20 is composed of a screw portion 20A and a heating portion 20B, and the screw portion 20A is 1 The opening screw 14 of the container (intermediate molded product 10A) is held by the grooved heating screw 21 of the shaft and the seven drive rolls 22, ..., And the screw molding groove 23 is fed as the container is fed by the screw rotation.
Thus, the opening flange 14 can be folded and continuously curled. That is, screw 2
Formed at 1 is a molding groove 23 whose cross-sectional shape continuously changes so that the curl can be finished into a predetermined shape as the process progresses. A heating unit 20B as shown in FIG. 6 is arranged in the front stage of the screw unit 20A, and the heating unit 20B is composed of a heating furnace 24. The container is uniformly heated and softened to achieve curling by the screw unit 20A in the rear stage. It has a structure that allows it. Here, in the heating furnace 24, a heater 25 is arranged around the passage of the container row, and a guide rod 26 for guiding the container row forward without contacting the heater 25 is arranged. .

By carrying out the curl treatment, the cut surface of the sharp mouth collar portion is hard to come into contact with the skin or the shrink film, and the effective width as the mouth portion can be secured, so that the strength is also maintained. On the other hand, the resin has the characteristic that the shape cannot be changed unless it is heated above a predetermined temperature, for example, above the softening temperature. The same applies to the case of performing the curl processing in the curl device 20 described above, and the heating furnace 24 is trying to achieve this. However, the above-mentioned curling device is generally industrially adapted to continuously process the containers, and in this case, the containers are stacked (hereinafter referred to as “stacked state”) in the heating section 20B and the screw section 20A. Be transported to. Therefore, the heating is uniformly applied to the portion other than the portion to be curled.

When a synthetic resin container has been deformed by heating in the past (in this case, molding by the above-mentioned male and female dies corresponds to this), residual stress is released and deformed when heated again. Cause Furthermore, when the temperature rises, the apparent elastic modulus decreases, so that the elastic member is deformed by its own weight. Styrene-based resin foam sheet container (hereinafter referred to as "PSP
The term `` container '') is more problematic and has the characteristic that it foams and deforms when heated in a heating furnace, and its thermal conductivity is extremely low compared to non-foamed synthetic resins. When the core part in the thickness direction is heated to a temperature suitable for curling deformation, the surface layer part is heated more than necessary, causing additional foaming and deformation, as well as foam cells rupturing and causing problems in appearance or strength. Will occur. Further, when heated over a wide area, only the relevant portion seems to swell, so that a remarkable deformation occurs in the appearance design.

Although there is such a problem in heating a synthetic resin container, particularly in a stacked state, a portion hidden by a container to be processed next is not heated, and a portion to be curled and a The section between the container to be processed is heated. Therefore, the side surface is deformed only in this heated portion. In particular, in the case of a foamed resin container, the side surface part of the container exposed on the surface side is additionally foamed and deformed, and if this deformation occurs, not only the finished appearance is bad, but also a step between the part that is not deformed and As a result, it becomes difficult to print on this portion, which causes a problem that the printing area on the side surface is reduced.

In particular, in the case of a PSP container, the tendency is remarkable as compared with a non-foamed container, and there is a problem that the cell itself does not swell or break, and further, a foamed sheet laminated by laminating a non-foamed resin on the surface. In the body, when the softening point of the non-foamed resin is high and the resin is inside the curl of the portion to be curled, heating from the outer surface does not provide sufficient heating, and the curl does not occur. In addition to the problem that it does not exist, it has been a factor to date that virtually no curling-treated foamed sheet container, particularly a high foaming ratio container having a high expansion ratio and a high heat insulating property is provided.

[0010]

As a result of extensive studies on a method for improving such a drawback, it is necessary to locally heat the mouth collar portion of the container to which the curl treatment is applied and to heat the portion other than the portion. Curling processability is remarkably improved by reducing to a minimum, heat deformation and the like can be reduced, curling can be performed easily even on a laminated molded product, and sufficient heating can be achieved for the curled portion. The present invention has been accomplished by finding out that the printing area can be secured.

That is, in view of the above situation, the present invention is to solve the problem by curling the mouth flange portion of the container downward or inward after locally heating the portion to be curled. It is a processing method to perform, while providing a safe synthetic resin container that does not damage lips etc. at the mouth and a method of curling the mouth of a synthetic resin container that secures the maximum printing area on the side surface, The point is to provide a local heating device for implementing the method.

[0012]

In order to solve the above-mentioned problems, the present invention has a container main body and an opening flange projecting to the outer periphery of the opening of the container main body, and the opening flange is curled. A method for curling the mouth of a synthetic resin container having a mouth portion formed by locally heating the opening flange and then curling the opening flange.

[0013] Here, it is more preferable that the back surface of the opening flange, which is the inner side, is locally heated by curling. Further, when the synthetic resin container is a foamed resin container, the effect of local heating according to the present invention is maximized. Further, when the foamed resin container is a deep container having a drawing ratio of 0.8 or more, which is represented by the height of the container / the diameter of the opening, the effect of the present invention is remarkable.

On the other hand, in order to realize the above-mentioned curling method, the opening flange protruding to the outer periphery of the opening of the synthetic resin container body is locally heated, and the opening flange is curled to form the mouth portion. Which is a local heating device for use in a synthetic resin, comprising at least one nozzle or outlet or slit having a width equal to or less than that of the opening flange so that hot air hits the back surface of the opening flange. A local heating device for the container was constructed.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, the synthetic resin used as the material of the container broadly refers to the resin produced industrially, but in this embodiment, the processing of the mouth collar part is more preferable in the synthetic resin. Description will be made by taking a difficult foam resin container as an example. Here, a sheet-shaped resin is used as the foamed resin, and a styrene-based resin foamed sheet is typical in a shallow container for food packaging such as instant noodles.

The styrene resin foamed sheet includes butane of polystyrene and copolymers of styrene and maleic anhydride, methacrylic acid, etc., and styrene resins such as mixed resins of these styrene resins and polyphenylene oxide. After kneading with a blowing agent such as chlorofluorocarbon and an extruder,
It is a foamed sheet extruded and foamed. Sheet thickness is 1
Generally, a sheet basis weight of 150 to 550 g / m ² is used, and a foaming ratio of 3 to 5 is preferable, but the range is not limited to this range. Further, a laminated styrene resin foam sheet obtained by laminating a non-foamed thermoplastic resin film on one side or both sides of the above styrene resin foam sheet and laminating them together can also be used.

As the non-foamed thermoplastic resin film laminated and laminated on the styrene resin foam sheet, styrene resins such as polystyrene and high impact polystyrene (HIPS), polyethylene, polypropylene (P
Olefin resin film such as P), polyvinylidene chloride, ethylene-vinyl alcohol copolymer resin,
Examples include individual and composite films of various gas barrier films such as polyester and polyamide. When the resin films are laminated on both sides, the same resin film may be used on both sides or separate resin films may be used.

As a method for laminating and compounding a thermoplastic resin film on a styrenic resin foam sheet, a method of dropping and laminating a film resin on a styrene resin foam sheet, a method of directly laminating a resin film with heat, and a method of laminating There is a method of laminating resin films via an adhesive. In the present embodiment, the styrene resin foam sheet and the laminated styrene resin foam sheet are both referred to as a styrene resin foam sheet when there is no particular need to distinguish between them.

A method of manufacturing the container 10 from the styrene resin foam sheet obtained by the above method will be described with reference to FIGS. First, as shown in FIG. 1, a styrene-based resin foam sheet 1 wound in a roll is heated through a heating furnace 2 to be secondarily foamed, and then a male and female mold 3 (in the figure, 3A is a female mold piece, 3B is The container body 11 is molded with a male mold piece, and the opening flange 14 having a horizontal portion 14A parallel to the bottom surface 13 is formed on the outer periphery of the opening 12 of the container body 11. The opening flange 14 is continuous with the surplus foam sheet 15 that does not participate in the molding of the container 10. Male and female molds 3 during this molding
The inside of the mold is decompressed by the vacuum evacuation means 4 to enhance the transferability of the mold shape. After molding the container body 11 and the opening flange 14,
The styrene-based resin foam sheet 1 is punched out with the automatic punching machine 5 equipped with a punching blade, a Thomson blade, or the like, leaving the opening flange 14 and an intermediate molded product 10A to be an individual container 10. The thickness of the obtained container is governed by the shape of the mold and the like and is not particularly limited, but is generally 1.5 to 2 mm.

Intermediate molded product 10A thus obtained
An example is shown in FIGS. 2 and 3. The inner peripheral side of the opening flange 14 of the intermediate molded product 10A shown in the figure is a horizontal portion 14A parallel to the bottom surface 13, and the tip portion 14B is inclined toward the bottom surface 13 side. The tip of the tip portion 14B of the opening flange 14 is a cut surface 14C punched vertically by the automatic punching machine 5.

The opening flange 14 is a portion which becomes a mouth portion by curling as will be described later, and in the one shown in FIGS. 2 and 3, the width of the horizontal portion 14A is set to the required width of the sealing surface. The width of the tip portion 14B is set to a width sufficient for curling. However, the shape of the opening flange 14 is not particularly limited in the present invention. In addition, in order to secure a sufficient sealing area on the upper surface of the mouth portion, the radius of curvature of the bent portion 16 where the container body 11 facing the opening 12 and the opening flange 14 intersect is made as small as possible. Is desirable.

The system of the local heating device 30 according to the present invention may be any one that can achieve local heating, but the back surface of the opening collar 14 to be heated, that is, from the outer peripheral direction in the normal heating furnace 24. If it is heating, it becomes a shadow from the perspective of the heater 25, and it is not preferable from the viewpoint of heat deformation to heat a portion other than the portion that is difficult to be heated due to the high heat insulating property of the styrene resin foam sheet 1. Therefore, it is required to have a mechanism for narrowing the heating range to at least the width of the opening flange 14. As a heating method, a ceramic heater that emits infrared rays or far infrared rays, a sheath heater, a heat ray irradiation by a quartz lamp or the like can be considered, but for the above reason, it is not possible to narrow the heating range to a few mm range with the present processing technology, which is preferable. Absent.

For the above reason, the hot air type is used as the heating source of the local heating device 30 of the present invention. Hot air
Suitable because the heating range can be controlled to some extent by changing the nozzle width that ejects it, and the medium that collides with the object to be heated is cooled relatively quickly, so it is unlikely to have a fatal temperature effect on parts other than planned. Is.

2 and 3 show the positional relationship between the hot air blowing portion 31 of the hot air type local heating device 30 and the opening flange 14, and FIG. 2 shows a single arc-shaped pipe 32 with one end closed. , Or a plurality of air outlets 33, ... Are arranged so as to face the rear surface side (lower surface side) of the opening flange 14, and FIG. 3 shows a nozzle 35 provided at the tip of the hose 34 as the hot air outlet 31. An example is shown in which it is arranged toward the back surface side (bottom surface side) of 14. That is, in any of the examples, the hot air having directivity can be blown to the inner portion by curling the opening flange 14. The nozzle 35 has an opening collar 14
A plurality may be arranged along the circumference of. Although not shown, a slit for blowing hot air may be formed along the arcuate pipe 32.

The outlet 33 or the nozzle 35 and the opening collar 1
It is preferable for the production management that the distance from the back surface of 4 is as close as possible, because hot air can reach the object to be heated while the temperature is not affected by the outside temperature, and there is no seasonal variation. But on the other hand,
Assuming curl processing of the opening flange 14 of the intermediate molded product 10A in the stacked state, when the air outlet 33 or the nozzle 35 is inserted more radially inside than the outermost diameter of the opening flange 14, the opening flange 14 comes into contact with the opening flange 14. It cannot be installed more than the diameter. This problem is solved by adding a mechanism for moving the blowout port 33 or the nozzle 35 for each one of the intermediate molded products 10A at an interval that does not interfere with the opening flange 14, but it is difficult to achieve in terms of mechanical trouble or cost. . Therefore, in the case where the opening flange 14 of the intermediate molded product 10A is curled in the stacked state, it is preferable to install the blowout port 33 or the nozzle 35 at the position where the outermost diameter is barely reached.

Further, the outlet 33 or the nozzle 35 is
Carefully position the back of the opening collar 14 to heat it,
You need to point it exactly. Therefore, a mechanism that can finely adjust the installation position of the pipe 32 in which the air outlet 33 is opened at a predetermined position, a mechanism that has a flexible structure for the entire hose 34 provided with the nozzle 35 or near the tip, and that freely adjusts the direction and distance, etc. Can propose.

The degree of heating by the local heating device 30 is determined by the temperature and the heating time. The heating time is
It cannot be limited because it depends on the material of the container.
However, in the case of a PSP container, when hot air of 400 ° C. or higher is blown at a close distance, bubbles are broken almost instantly, so that it is difficult to practically use it. Moreover, since PSP does not soften at a temperature of 80 ° C. or lower, it is not effective as an auxiliary heating device. Further, the air volume may be such that it can transfer a certain amount of heat or more. Generally, low flow rate should be specified for high temperature medium, and high flow rate should be specified for low temperature medium. Even at a temperature of 80 ° C., if 500 liters / min or more is used, unexpected deformation may occur. The flow rate can be easily controlled by installing a damper, a pressure control valve (with a waste gate), a relief valve, or the like on the upstream side of the air outlet 33 or the nozzle 35.

The heating time is controlled by the time for which the blown medium is applied, generally the number of outlets 33 or nozzles 35. For local heating, it is necessary to install at least one or more blower outlets 33 or nozzles 35. However, a method of increasing or decreasing this number to select a heating time, or an opening collar 14
In the case of providing a slit-shaped blowing hole along the shape of, the method of selecting the heating amount / time is also proposed.

Temperature / heating amount / in the local heating device 30
For the above reason, it is difficult to concretely limit the hot-air blowing unit 31 because it varies depending on the material and shape of the container, and the degree of heating in the heating unit 20B in the preceding stage, the curling speed, the distance to the container, and the container It is a factor that should be considered individually depending on the material, but the following are examples if it is intentionally taken into consideration. For example, in the case of a polystyrene foam container (PSP container) having HIPS on the outer surface of about 50 μm, the intermediate molding is performed by staying for 5 seconds in the heating furnace 24 of the curl device 20 at an atmospheric temperature of 300 ° C. and proceeding at about 40 rpm. In the case of further locally heating the article 10A, one air outlet 33 or nozzle 35 having a diameter of about 8 mm is placed at a distance of 10
It was preferable to apply hot air of about 240 liters per minute at an outlet temperature of about 350 ° C. from the position of mm toward the back surface of the opening collar 14.

Further, the local heating device 30 of the present invention will be described in detail. As shown in FIG.
Is incorporated inside the curl device 20, and its position is installed between the screw part 20A and the heating part 20B of the curl device 20. FIG. 10 is a specific example of the local heating device 30 shown in FIG. 2, in which an arc-shaped pipe 32 having one or a plurality of outlets 33 is connected to the tip of a heat insulating pipe 36, and the pipe 36 is also provided. An air damper 37 is provided at the position so that the flow rate can be adjusted. Further, FIG. 11 is a specific example of the local heating device 30 shown in FIG. 3, in which the nozzle 35 is provided at the tip of the heat insulating pipe 36 as described above.
While connecting the flexible hose 34 having
Similarly, the pipe 36 is provided with an air damper 37 so that the flow rate can be adjusted. In this case, the flexible hose 34 is bendable, can maintain its state, and the direction and position of the nozzle 35 can be set arbitrarily.

In the present invention, the portion to be locally heated is the portion to be curled (opening collar 14).
In the case of the SP container, since the heat insulating property is high, it is possible to obtain better curl workability by making it possible to heat mainly the portion inside the opening flange 14 that is not sufficiently heated in the heating furnace 24. This can be easily achieved by adopting, for example, the hot air system using the pipe 32 provided with the above-mentioned air outlet 33 or the tapered nozzle 35. In addition, in order to prevent swelling other than the above-mentioned desired part, a heat shield device such as a shield plate made of a heat insulating material is provided along with the local heating device 30, and a container part other than the desired part is unnecessary. It is preferable to take preventive measures so as not to be heated. Conveniently, it is achieved by coating the non-heated part with a heat insulating material.

By using the above local heating method, it is possible to perform curl treatment with good workability without exerting a thermal influence on an unnecessary portion in the synthetic resin container. To perform this curl processing, for example, the curl device 20 manufactured by Brown Co. shown in FIGS. 4 to 7 is used. Since the structure of the curl device 20 is as described above, the description thereof will be omitted.
As shown in FIG. 7, the intermediate molded products 10A, ...
Are successively fed by the heating screw 21 and the driving rolls 22, ...
The container 10 having the mouth portion 17 which is curled by the molding groove 23 of FIG. The mouth 17 of the container 10 is illustrated in FIG. In this case, the horizontal portion 14A of the opening flange 14 becomes a flat seal surface 17A for sticking a seal lid (not shown), and the tip cutting surface 14C approaches the side surface of the container body 11,
Even if a lip or the like is applied to the mouth portion 17, there is no possibility of contacting the cut surface 14C.

[0033]

[Example] The basis weight before molding was 720 g / m ² (inner surface: P
P30 μm / intermediate layer: PSP basis weight 500 g / m ² / outer surface: HIPS 200 μm), a molded product shape is imparted by meshing of the male and female dies 3, and a surplus foamed sheet is formed by the automatic punching machine 5. Punched from 15, mouth diameter 97 mm, bottom diameter 60 m
m, height 100 mm, drawing ratio about 1, basic thickness 2 mm P
An SP container (intermediate molded product 10A shown in FIGS. 2 and 3) was prepared, and a curl treatment was tried using the curl device manufactured by Brown Co., USA.

Here, the overall outer diameter of the opening collar 14 before curling is 98 mm, and the width of the horizontal portion 14A is about 2.
The width of the tip portion 14B is 2 m as a folding margin.
m. The angle of the folding margin (tip portion 14B) was set to 80 ° with respect to the horizontal plane. At this time, the horizontal portion 14
It was slightly compressed so that the thickness of A was about 1.2 mm.

Then, after gently heating the entire intermediate molded product 10A by the heating furnace 24, the local heating device 30 is used.
Only the back surface (lower surface) of the opening flange 14 was locally heated by the (hot air nozzle 35).

The general settings of the curl device 20 are as follows.・ Heating furnace atmosphere temperature setting 300 ℃ ・ Screw temperature setting 90 ℃ ・ Heating time about 5 seconds

On the other hand, a local heating device was arranged in the vicinity of the opening flange 14 to be curled. The arrangement conditions were set as follows.・ Method Hot air heating ・ Nozzle diameter 8 mm ・ Air flow 240 liters / min ・ Temperature 350 ° C at nozzle ・ Temperature approx. 10 mm ・ Nozzle number 2 ・ Direction Curling part back surface heating direction (see Fig. 3)

Then, comparative tests were carried out with and without the use of the hot air heating. When not using hot air heating,
The heating furnace temperature was 350 ° C. As a result of a plurality of tests, when hot air heating was not used, cracks occurred in the mouth portion and swelling occurred in the side surface portion of the container body. On the other hand, when hot air heating was used, cracks did not occur in the mouth portion, swelling did not occur in the side surface portion of the container body, and a good mouth portion of the container was formed.

When the local hot air heating was not adopted, the heating furnace temperature was raised to perform the curling in order to achieve the curling.
Even in this case, the back surface temperature of the portion to be curled did not rise sufficiently, and the crack occurred when the curling was attempted. Further, the side surface portion of the container body was swollen by heating in the heating furnace, and a clear difference in shape was generated between the side surface portion and the non-heated portion.

When the local heating device was used, the overall temperature applied in the heating furnace could be suppressed to a low level, so that the side surface did not swell. Further, since the back surface of the curling portion was also sufficiently heated, molding defects such as cracks did not occur, and molding could be achieved with good curl workability.

[0041]

According to the method for curling the mouth of the synthetic resin container of the present invention as described above, the curl characteristic of the opening collar serving as the mouth is improved by utilizing the present invention based on the test results. The mouth part having a good appearance could be curled. Further, only the back surface of the opening collar to be curled by the local heating device of the present invention can be locally heated, and good curling can be performed without causing thermal deformation to other parts such as the wall surface of the container body. Could be done.

[Brief description of the drawings]

FIG. 1 is a simplified layout view showing a part of a container manufacturing apparatus according to the present invention.

FIG. 2 is a partial cross-sectional view showing the positional relationship between an intermediate molded product before curling and the outlet of a hot air outlet.

FIG. 3 is a partial cross-sectional view showing a positional relationship between an intermediate molded product before curling and a nozzle of a hot air blowing portion.

FIG. 4 is an abbreviated perspective view showing a screw portion of a curl device.

FIG. 5 is a partial side view of the heating screw.

FIG. 6 is a partial cross-sectional view showing the relationship between the heating unit of the curl device and the intermediate molded product in a stacked state.

FIG. 7 is a partial cross-sectional view showing a state in which the opening flange of the intermediate molded product in the stacked state is curled by the screw part to mold the mouth part.

FIG. 8 is an enlarged sectional view of a mouth portion curled according to the present invention.

FIG. 9 is an abbreviated front view showing the relationship between a local heating device and a curl device.

FIG. 10 is a partial side view showing a specific example of a local heating device provided with the hot air blowing part shown in FIG.

FIG. 11 is a partial side view showing a specific example of a local heating device provided with the hot air blowing part shown in FIG.

[Explanation of symbols]

 1 Styrene Resin Foamed Sheet 2 Heating Furnace 3 Mold 3A Female Mold Piece 3B Male Mold Piece 4 Vacuum Evacuation Means 5 Automatic Punching Machine 10 Container 10A Intermediate Molded Product 11 Container Body 12 Opening 13 Bottom 14 Opening Collar 14A Horizontal Part 14B Tip Part 14C Cutting surface 15 Surplus foamed sheet 16 Bending part 17 Mouth part 17A Sealing surface 20 Curl device 20A Screw part 20B Heating part 21 Heating screw 22 Drive roll 23 Forming groove 24 Heating furnace 25 Heater 26 Guide rod 30 Local heating device 31 Hot air blowing Part 32 Pipe 33 Air outlet 34 Hose 35 Nozzle 36 Piping 37 Air damper

Claims (5)

[Claims] 1. A synthetic resin container comprising a container body and an opening flange projecting from an outer periphery of an opening of the container body, wherein the opening flange is curled to form a mouth portion. A method for curling a base of a synthetic resin container, which comprises locally heating the opening flange and curling the opening flange. 2. The curling method for a mouth portion of a synthetic resin container according to claim 1, wherein the back surface of the opening flange, which is the inner side, is locally heated by curling. 3. The method for curling the mouth of a synthetic resin container according to claim 1, wherein the synthetic resin container is a foamed resin container. 4. The curling method for a mouth portion of a synthetic resin container according to claim 3, wherein the foamed resin container is a deep container having a drawing ratio of 0.8 or more, which is represented by a container height / a diameter of an opening. 5. A local heating device for locally heating an opening flange projecting to the outer periphery of an opening of a synthetic resin container body and curling the opening flange to form a mouth portion,
A local portion of a synthetic resin container, characterized in that at least one nozzle or outlet or slit having a width equal to or less than that of the opening flange so that hot air is blown against the back surface of the opening flange is provided. Heating device.