JPH03289462A - Plastic container and its sealing method - Google Patents

Abstract

PURPOSE:To permit a container to be accurately sealed even if its contents are viscous by a method wherein the flange of a lid is pressed against the opening edge of the container all around its periphry at a predetermined width while heating the thermoplastic resin layer of the lid flange, the molten thermoplastic resins are thus forced out to the inner and outer peripheral sides and such molten resins are thereafter cooled. CONSTITUTION:A container 20 is provided at its opening edge with a flange 23 projecting slightly outward. The container 20 which has been filled with its contents is covered with a lid 2 by fitting the flange 2b of said lid over the flange 23 of the container 20. Such assembled body is pressed while high-frequency waves are being applied thereto, whereby the thermoplastic resin layers 6 of gas-barrier multilayer films 4 and 8 are heated into a molten state between the upper face 23a of the flange 23 and the lid flange 2b. During this treatment, the molten resin of the thermoplastic resin layers 6 are forced out from the pressed part and flow into a resin escape space 32 formed by a sloping part 31 and onto the inner peripheral surface 23c of the flange 23. The high-frequency heating is thereafter stopped to cool the molten resin.

Description

DETAILED DESCRIPTION OF THE INVENTION "Field of Industrial Application" The present invention relates to a plastic container that can be retorted and whose contents can be stored for a long period of time, and a method for sealing the same.

``Prior Art'' Metal cans have been widely used as containers for long-term storage of foods. However, there are problems with metal cans, such as the need for force to open them and the risk of cutting your fingers.

The present inventors have proposed an easy-to-open plastic container that can solve the above-mentioned problems and is also excellent in terms of design freedom (for example, Japanese Patent Application No. 60-34649, Japanese Patent Application No. 61-203335). No. 63-251871).

This easy-to-open sealed container is composed of a container body 1 and a lid 2, as shown in FIG. The container body l has a gas barrier material 4 on the inner surface of a rigid outer layer 3 made of thermoplastic resin.
are laminated. A flange 13 extending outward is formed at the opening side end of the container body l.

The gas barrier material 4 is laminated from the inner peripheral surface 1a of the container body 1 to the upper surface 13a of the flange 13. As shown in FIG. 1O, the gas barrier material 4 is made by laminating thermoplastic resin layers 66 made of unstretched polypropylene film on both sides of an aluminum foil 5 having gas barrier properties.

The lid 2 is formed by laminating a gas barrier material 8 having gas barrier properties on the inner surface of an outer layer portion 7 made of thermoplastic resin. The gas barrier material 8 includes the gas barrier material 4 of the container body l.
The same thing is used. This lid 2 is formed of a central portion 2a that is dropped into the opening of the container body J, and a flange portion 2b that fits into the opening side end of the container body I.

The flange portion 2b is formed to have a U-shaped cross section so as to tightly wrap around the flange portion 13 of the container body l, and the outer peripheral portion thereof is used as an escape prevention portion 2C. Further, a weakened line 9 where the gas barrier material 8 is exposed is formed at a position along the outer peripheral edge of the central portion 2a of M2.

In order to close the container body l of this easy-to-open sealed container with the lid 2, after filling the contents, fit the flange part 2b of the lid 2 into the flange part 13 of the container body l, and then weld this with the high frequency welding device. It is sandwiched between the oscillation coil 15 and the push-up plate 16 and high-frequency welded. At this time, the container main body 1 is deformed so that the diameter of the opening expands, but in this container, the outer circumferential surface 13c of the flange 13 hits the escape prevention part 2c of the flange 2b of the lid 2, preventing the opening from expanding in diameter. be done.

FIG. 11 shows an enlarged view of the actually welded part between the container body 1 and the lid 2 of this container.
The gas barrier material 4 and the thermoplastic resin layer 6.6 of the gas barrier material 8 of the lid 2 are linearly pressed and fused together along the inner peripheral edge 13b of the flange 13 of the container body l. As a result, the container body 1 is in a sealed state with the lid 2.

``Problems to be Solved by the Invention'' In the conventional sealing methods and plastic containers, there was a problem to be solved in that sealing failures tend to occur when the contents are viscous.

That is, when a part of the contents adheres to the upper surface 13a of the flange 13 of the container body 1 when filling the container body 1 with the contents,
Even if this is removed with an end face cleaner or the like, it cannot be completely removed if the contents are viscous. When the lid 2 is attached to the container body 1 and sealed in such a state, the container body 1 and M2 cannot be brought into close contact with each other in the area where the residual contents are present, resulting in a sealing failure. This in turn leads to spoilage of the contents.

The present invention was made in view of the above circumstances, and an object of the present invention is to provide a sealing method and a plastic container that can reliably seal even the contents are viscous.

"Means for Solving the Problems" In the sealing method of the present invention, pressure is applied to the upper surface of the opening end of the container body and the thermoplastic resin layer on the flange of the lid at a predetermined width over the entire circumference while heating the thermoplastic resin layer. , the molten thermoplastic resin is extruded to the inner and outer circumferential sides, and then the molten resin is cooled, thereby welding the top surface of the container body and the flange of the lid to a predetermined width over the entire circumference. At the same time, the above-mentioned object was achieved by forming a resin reservoir seal portion in which the container body and the lid were bonded together using extruded resin on the inner and outer circumferential sides of the fused portion.

When the flange portion formed on the lid abuts not only the upper surface side of the opening side end of the container body but also the inner circumferential surface thereof,
The part to which pressure is applied during pressure welding is a part of a predetermined width extending outward from the inner peripheral edge of the open end of the container body, and the inner resin pool seal part is applied to the inner peripheral surface of the open end of the container body. It is good to form.

In addition, when applying the above method to a plastic container with a lid having a flange portion having a U-shaped cross section that comes into contact with the outer peripheral surface, top surface, and inner peripheral surface of the opening side end of the container body, the opening side end of the container body It is preferable to form a space for the resin to escape so as to be located on the outer circumferential side between the part and the flange part of the lid.

In addition, when applying the above method to a plastic container having an outwardly extending flange at the open end of the container body, after overlapping the flange of the container body and the flange of the lid,
While heating the thermoplastic resin layer of the flange and the flange, it is preferable to press the inner periphery of the flange and the flange while avoiding applying force to the outer periphery of the flange.

Furthermore, as the heating method, preferably a high frequency induction heating method is employed. In heat transfer methods from outside the container, such as hot plate seals, the meltable plastic layer between the barrier layer of the lid and the main body is heated, and when the pressing force is increased, the outside of the container deforms.In contrast, the high-frequency induction heating method described above When the barrier layer is made of metal, the external resin temperature is lower than the molten resin temperature between the barrier layers, and there is no fear of deformation.

"Function" In the plastic container of claim 1, since a resin escape space is formed on the outer peripheral side between the opening end of the container body and the flange of the lid, the opening of the container body expands in diameter during welding. Even if an escape prevention part is formed on the flange part of the lid to surround the outer circumferential surface of the open end of the container body in order to prevent this, the molten resin can flow outward from the pressure-welded part.

In the sealing method according to claim 2, when welding the container body and the lid, the upper surface of the container body and the flange portion of the lid are pressed together at a predetermined width, and the molten resin in that portion is transferred to the inner peripheral side,
The molten resin flows in large quantities as it is pushed toward the outer periphery, and the foreign matter rides this flow and is removed from the pressure welded part.

Then, the container body and the lid are integrated by the resin pool seal portion made of resin extruded from the pressure welded portion and the pressure welded portion.

According to the sealing method of claim 3, during welding, pressure is applied to a portion of a predetermined width extending outward from the inner peripheral edge of the opening side end of the container body, so that the sealing material is pushed inward from the pressure-welded portion. The resin flows to the inner circumferential surface of the open end of the container body and forms a resin pool seal there. When a resin pool seal is formed on the inner peripheral surface of the opening side end of the container body in this way,
The resin pool seal portion can prevent the lid from being pushed up.

In the sealing method of claim 4, the inner circumferential side of the flange formed on the container body is pressure-welded without applying any force to the outer periphery of the flange, so that the outer periphery of the flange can be displaced. By displacing the outer circumference of the flange, a space is formed between the flange of the container body and the flange of the lid, into which the molten resin can flow.

EMBODIMENT OF THE INVENTION Hereinafter, the plastic container of the present invention and its sealing method will be described in detail with reference to the drawings. Note that the same components as those in the conventional example are given the same reference numerals to simplify the explanation.

FIGS. 1 and 2 show the main parts of a plastic container manufactured by the sealing method of the present invention.

This plastic container is composed of a cup-shaped container body 20 and a lid 2 having a flange portion 2b.

A gas barrier material 4.8 is laminated on the inner surfaces of the container body 20 and the lid 2.

A flange 23 that bulges slightly outward is formed at the opening side end of the container body 20 of this plastic container. A chamfered portion 31 cut diagonally is formed on the outer peripheral edge of the flange 23, and when the container body 20 and the lid 2 are combined, the flange 23 of the container body 20 and the flange of M2 are formed by this chamfered portion 31. A resin escape space 32 between the part 2b and the part 2b.
is starting to form.

In this plastic container, a portion between the inner circumferential edge 23b of the upper surface 23a of the flange 23 of the container body 20 and the resin escape space 32 is fused to the M2 flang g2b in a press-welded state, and this portion is press-welded. It is section 33. Further, a resin pool seal portion 34 is formed between the inner circumferential surface 23c of the flange portion 23 and the resin escape space 32, where the container body 20 and M22 are bonded together with the resin that is extruded when the pressure-welded portion 33 is formed. 35 is formed.

Next, the sole method for this plastic container will be explained.

In this sealing method, M2 is first placed over the container body 20 filled with contents, and the flange portion 23 of the container body 20 and the flange portion 2b of the lid 2 are fitted together.

Then, this assembly is sandwiched between a flat plate-shaped high-frequency oscillation coil 15 and a push-up plate 16 of a high-frequency welding device, and pressure is applied while applying high-frequency waves. Then, the upper surface 2 of the flange 23 of the container body 20
3a and the flange portion 2b of the lid 2, the thermoplastic resin layers 6, 6 of the gas barrier multilayer film 4.8 are heated and melted. Further, a portion between the inner circumferential edge 23b of the flange portion 23 and the chamfered portion 31 is pressed against the flange portion 2b of the lid 2. When the container body 20 and the lid 2 are pressed together in this way, a force is applied to the container body 20 to enlarge the diameter of the opening, but the deformation of this opening is caused by M
This is prevented by the outer peripheral surface 23d of the flange 23 of the container body 21 coming into contact with the escape prevention part 2c provided on the flange 2b of No. 2.

This high frequency welding process is performed until the thickness of the thermoplastic resin layer 6.6 of the gas barrier materials 4, 8 or the pressure welded portion 33 becomes approximately 1/2 or less of the thickness before welding. During this process, the molten resin of the thermoplastic resin layers 6, 6 is extruded from the pressed parts, and the resin escape space 32 formed by the chamfered part 31 of the container body l and the container body 20 are pushed out. The liquid flows to the inner circumferential surface 23c of the collar portion 23.

After that, when heating by high frequency is stopped and the molten resin is cooled, the upper surface 23a of the container body 20 and the M2
A press-welded portion 33 is formed by press-welding the flange portion 2b over the entire circumference with a predetermined width. Furthermore, resin pool seal parts 34 and 35 are formed on the inner and outer peripheral sides of this press-welded part 33 by extruded resin to which the container body 20 and M2 are adhered.

The method of sealing the plastic container of this embodiment is to
This is a method of applying pressure to a predetermined width over the entire circumference of the thermoplastic resin layer 6.6 present in the container body 20 and the lid 2 by pushing out the molten resin to the inner and outer circumferential sides. , when the container body 20 is filled with the contents, the container body 20
Even if viscous contents remain on the upper surface 23a of the flange 23,
This residual content is carried by the flow of molten resin during high-frequency welding and is removed to the inner or outer circumferential side of the press-welded portion 33. As a result, the pressure welded part 3 is sealed without any contents remaining.
3 will be welded.

The present inventors consider this phenomenon as follows. That is, the thermoplastic resin layer 6 of the gas barrier material 48 is in contact with the upper surface 23a of the container body 20 and the flange portion 2b of the lid 2.
．． When 6 is melted and pressure is applied, the interface portions of the molten resin that contact each other are quickly pushed inward or outward. Therefore, the contents remaining at the interface are smoothly pushed inward or outward by the flow of the resin. Then, the upper surface 23a of the container body 20 and the flange portion 2 of the lid 22
A new resin interface is gradually formed in the pressed portion.

Therefore, according to this sealing method, the safe container main body 20 and the lid 2 can be reliably brought into close contact over the entire circumference, and the reliability of sealing the plastic container can be improved.

Further, according to this sealing method, the resin extruded from the pressure welded part 33 forms resin pool seal parts 34 and 35 on the inside and outside of the pressure welded part 33, and even in this part, the container body 20 and the lid 2 are sealed. Since it is integrated, the container body 20
The adhesive strength between the container and the lid 2 is increased, and the sealing performance of the container can also be improved in this respect.

Furthermore, in this sealing method, pressure is applied to a predetermined width portion outward from the inner peripheral edge 23b of the flange 23 of the container body 20, so that the resin that moves inward from the melted resin during high-frequency welding is absorbed into the container. It is pushed out toward the inner circumferential surface 23c of the flange 23 of the main body 20. Therefore, the lid 2 can be prevented from being pushed upward by the inner resin pool seal portion 34 formed by the extruded resin. Therefore, according to this sealing method, the container body 20 and the lid 2 can be sealed more reliably.

Furthermore, in the plastic container of this embodiment, the container body 20
A chamfered portion 31 is formed on the outer peripheral edge of the flange 23 of the container body 20 to provide a resin escape space 32 between the upper surface 23a of the container body 20 and the M2 flange portion 2b. Even if it is surrounded by the flange portion 2b of the lid 2 having a U-shaped cross section, the outward flow of the molten resin is not inhibited. Therefore, in this plastic container, the contents remaining on the upper surface 23a of the container body 20 can be smoothly removed outward from the press-welded portion 33 during high-frequency welding, and highly reliable sealing can be achieved.

(Example 2) A container body 50 shown in FIGS. 3 and 4 differs from the container body 20 illustrated in Example 1, in that the flange portion 53 is formed wide.

When sealing such a container body 50 with the lid 5I, it has been necessary to arrange a push-up plate 16 under the flange 53 in order to apply uniform pressure in the usual method. In this embodiment, after the flange part 53 of the container body 50 and the flange part 52 of the lid 51 are overlapped, the flange part 52 of the container body 50 is pressed by the high frequency oscillation coil 15 of the high frequency welding device and the push-up plate 16 from the bottom of the container body. The inner circumferential portion of the collar portion 53 and the flange portion 52 were pressed while avoiding any force being applied to the outer circumferential portion of the portion 53. As a result, the thermoplastic resin between the barrier materials in the inner portion of the collar portion 53 was pushed inward and outward. The resin pushed outward displaces the outer peripheral portion of the collar portion 53 that is not pressed downward and accumulates in this portion.

After that, when the molten resin was cooled, the upper surface 5 of the flange 53 of the container body 50 was exposed to the inner circumference of the pressed flange 53.
3a and the flange portion 52 of the lid 51 are welded together to form a pressure welded part 33, and a resin pool part 34 where the container body 50 and the lid 51 are bonded by the resin pushed in and out of this pressure welded part 33. , 35 were formed.

In this sealing method, high-frequency welding is performed without applying any pressing force to the outer circumference of the wide flange 53 provided on the container body 50, so that the molten resin displaces the outer periphery of the flange 53 downward. It flows here. Therefore, according to this sealing method, as in the case of the first embodiment, the molten resin can be smoothly pushed outward, and the remaining contents can be smoothly removed from the pressure welded part 33 during high frequency welding.

When a push-up plate is placed under the flange as in the conventional method, the pressure is applied uniformly, so there is almost no discharge of resin from the pressure-welded melted part, and therefore the resin pool 3
4.35 will not occur.

(Example 3) FIG. 5 shows a plastic container of Example 3.

This plastic container differs from that of Example 1 in that the gas barrier material 4 is not laminated on the container body 20, but the plastic outer layer 3 of the container body 20 is directly welded to the lid 2. be.

Even in such a plastic container, highly airtight sealing can be performed in the same manner as in Example 1.

7 Experimental Example” (Experimental Example 1) The plastic container of Example 1 was prototyped and a pressure leak test was conducted. For comparison, a similar test was conducted on the conventional plastic container shown in FIG.

The test method is as follows.

First, as shown in Figure 6, connect air gun 6 to M2 of the container.
0 nozzle is inserted, and then air is fed into the water tank to pressurize it, as shown in FIG. The pressure at the time when air leakage occurred was defined as the internal pressure resistance strength.

As a result of this test, the material of Example 1 showed an internal pressure resistance of 2.3 kg, while the material of the conventional example had an internal pressure resistance of 1.7 kg.

(Experimental Example 2) Next, the upper surface 23a of the flange 23 of the container body 20 of Example 1
M2 was sealed with crab meat (linear with a diameter of 0.3 mm) placed on it and subjected to a penetrating liquid (red check) test. For comparison, a conventional plastic container was also subjected to the same test.

The test method for the penetrant test is as follows.

First, the bottom of the container is cut into rounds using a cutter as shown in FIG. 8, and then the contents are removed from the container and washed. Next, after making sure that there is no water etc. inside the container, the container body 20 is removed.
The penetrating liquid is sprayed from the inside of the area where the lid 2 and the lid 2 come into contact. Leave it in this state for at least 1 hour, and then dry it in a dryer for at least 4 hours.

After confirming that the penetrating liquid has dried, the sandwiched portion of the crab meat is cut out with a cutter and observed under magnification. Of the 100 cans tested, the number of cans in which the penetrating liquid had penetrated into the pressure welded portion 33 was defined as the number of leaks.

As a result, in the case of Example 1, the number of leaks was 0, whereas in the case of the conventional example, crab meat remained in the pressure-welded portion, and the number of leaks was 45 cans.

From the results of Experimental Examples 1 and 2, it was confirmed that the seal of Example 1 had high reliability.

(Experimental Example 3) The internal pressure resistance strength of the Plus Deck container of Example 3 shown in FIG. 5, in which the gas barrier material 4 was not laminated on the inner peripheral surface of the container body 50, was investigated. For comparison, the same applies to a conventional container using a container body without a gas barrier material layered thereon (the conventional container shown in Fig. 9, in which the gas barrier material 4 is not layered on the container body L). The internal pressure resistance strength was investigated.

As a result, the internal pressure strength of the container of the comparative example was 1.1 kg. On the other hand, the material of Example 3 exhibited an internal pressure resistance of 1.6 kg. From the results of this test, it was confirmed that even when the gas barrier material 4 was not laminated, the container body 20 and the lid 2 could be firmly welded together according to the sealing method of the present invention.

"Effects of the Invention" As explained above, the plastic container of claim 1 is one in which a resin escape space is formed so as to be located at the outer peripheral portion between the opening side end of the container body and the flange of the lid. In order to prevent the diameter of the opening of the container body from expanding, even if an escape prevention part is formed on the outer circumferential surface of the opening end of the container body or on the flange of the lid, there will be no leakage from the molten resin or pressure-welded part. Can flow outward. Therefore, in this plastic container, the contents remaining on the upper surface of the container body can be smoothly removed outward from the press-welded portion during high-frequency welding, and highly reliable sealing can be achieved.

The sealing method according to claim 2 includes heating the thermoplastic resin layer on the upper surface of the open end of the container body and the flange portion of the lid while applying pressure in a predetermined width over the entire circumference, thereby filling the molten thermoplastic resin inside. The molten resin is extruded to the circumferential side and the outer circumferential side, and then the molten resin is cooled, whereby the upper surface of the container body and the flange part of the lid are pressure-welded to a predetermined width over the entire circumference, and the pressure-welded part is Since this method uses extruded resin to form resin pool seals on the inner and outer sides, where the container body and lid are bonded, a large amount of molten resin from the press-welded area is swept away to the inner and outer sides. As a result, contaminants are removed from the pressure welded part. Therefore, according to this sealing method,
Even if the contents remain on the top surface of the open end of the container body when filled with viscous contents, the container body and lid can be reliably welded around the entire circumference, making it possible to seal plastic containers. reliability can be improved.

In addition, according to this sealing method, the resin extruded from the pressure welded part forms a resin pool seal part on the inside and outside of the pressure welded part, and the container body and the lid are integrated in this part as well. The adhesive strength between the container body and the lid increases, and the sealing performance of the container can also be improved in this respect.

In the sealing method of claim 3, the part to which pressure is applied during pressure welding is a part of a predetermined width extending outward from the inner peripheral edge of the opening side end of the container body, so that the pressure is pushed inward from the pressure welded part. The resin flows to the inner circumferential surface of the open end of the container body and forms a resin pool seal there. Therefore, according to this sealing method, it is possible to prevent the lid from being pushed up by the resin pool seal portion formed on the inner side. Therefore, according to this sealing method, the container body and the lid can be more reliably welded.

In the 7-ring method of claim 4, the inner circumferential portion of the crocodile portion of the container body and the flange portion of the lid are pressed and welded together while avoiding the application of force to the outer circumferential portion of the flange portion of the container body. The outer periphery is movable. Therefore, in this sealing method as well, the resin melted and extruded during pressure bonding can flow to the outer circumferential side of the flange portion, and the remaining contents can be smoothly removed from the pressure bonding and welding portion.

[Brief explanation of the drawing]

Fig. 1 is an enlarged cross-sectional view of part A in Fig. 2, Fig. 2 is a cross-sectional view of the plastic container of Example I, and Fig. 3 shows the state of the plastic container of Example 2 before being sealed. 4 is a sectional view showing the plastic container of Example 2, FIG. 5 is a sectional view showing the plastic container of Example 3, and FIGS. 6 and 7 explain the pressure leak test method. 8 is a schematic diagram for explaining the penetrant test method, FIG. 9 is a sectional view showing a conventional plastic container, and FIG. 10 is a sectional view showing a gas barrier material.
FIG. 11 is an enlarged cross-sectional view of section B in FIG. 9. FIG. 2. Lid, 2b. Flange portion, 2c Escape prevention portion, 6. Thermoplastic resin layer, 20. Container body, 23. Tsubabe, 23a・
Top surface, 23 b - inner peripheral edge, 23 c inner peripheral surface, 32 - resin escape space, 33 - pressure welded part, 34. 35 - resin pool seal part, 50 container body, 51 lid, 52 - flange part, 53 - Flange, 53a, top surface.

Claims (4)

[Claims] (1) A cup-shaped container body having a thermoplastic resin layer on the upper surface of the opening end, and a U-shaped cross section or an upper surface that abuts the outer peripheral surface, upper surface, and inner peripheral surface of the opening end of the container body; It consists of a lid that has a flange with an inverted L-shaped cross section that comes into contact with the inner circumferential surface and a thermoplastic resin layer on the lower surface of the flange. A plastic container in which the container main body and the lid are integrated when used, and a space for resin escape is formed on the outer peripheral side between the opening side end of the container main body and the flange part of the lid. When the upper surface of the open end of the container body and the flange of the lid are fused together, the resin extruded from this part is transferred to the resin escape space and the inner periphery of the open end of the container body. A plastic container characterized in that the resin can flow into the surface portions to form a resin pool seal portion in these portions. (2) A cup-shaped container body having a thermoplastic resin layer on the upper surface of the opening side end, and a flange portion that comes into contact with the upper surface of the opening side end of the container body, and a thermoplastic resin layer on the lower surface of the flange portion. A method for sealing a plastic container consisting of a lid having layers, in which the top surface of the container body and the flange portion of the lid are overlapped, and then the top surface and the flange portion are heated. While heating the plastic resin layer, pressure is applied to the entire circumference in a predetermined width to push out the molten resin to the inner and outer circumferences.Then, the molten resin is cooled, which causes the upper surface of the container body and the lid to The flange portion is fused to a predetermined width over the entire circumference, and a resin pool seal portion is formed on the inner and outer periphery sides of the fused portion, where the container body and lid are bonded using extruded resin. A method for sealing a plastic container, characterized by: (3) A cup-shaped container body having a thermoplastic resin layer on the upper surface of the opening end, and a flange portion that abuts the upper surface and inner peripheral surface of the opening end of the container body, and the lower surface of the flange portion. A method for sealing a plastic container comprising a lid having a thermoplastic resin layer on the top, the container body and the lid being integrated, the top surface of the container body and the flange portion of the lid are overlapped, and then these top surfaces and While heating the thermoplastic resin layer of the flange part, pressure is applied to a predetermined width part outward from the inner circumferential edge of the open end of the container body over the entire circumference, and the molten resin is applied to the inner circumferential side and outward. The molten resin is extruded toward the outer periphery, and then the molten resin is cooled, whereby the upper surface of the container body and the flange portion of the lid are fused together over the entire circumference at a portion of a predetermined width extending outward from the inner periphery of the upper surface. At the same time, a resin pool seal portion is formed on the outer periphery of the upper surface of the opening side end of the container body and the inner periphery of the opening side end of the container body, in which the container body and the lid are bonded by the extruded resin. A method for sealing plastic containers characterized by: (4) A cup-shaped container body having an outwardly extending flange formed at the opening side end and a thermoplastic resin layer formed on the upper surface of the flange, and the upper surface and inner periphery of the flange of the container body. A method for sealing a plastic container comprising a lid having a flange portion that comes into contact with a surface and a thermoplastic resin layer on the lower surface of the flange portion, the method comprising: After overlapping the flange portion and the flange portion of the lid, while heating the thermoplastic resin layer of the flange portion and the flange portion, the inner periphery portion and the flange portion are heated while avoiding applying force to the outer periphery of the flange portion. The molten resin is pressed onto the outer circumference of the flange and the inner periphery of the open end of the container body, and then the molten resin is cooled and solidified, thereby forming the upper surface of the flange of the container body and the flange of the lid. At the same time, the extruded resin is applied to the outer circumference of the flange of the container body and the inner circumference of the opening end of the container body. A method for sealing a plastic container, comprising forming a resin pool seal portion to which a lid and a lid are adhered.