JP2011042107A - Method of manufacturing hollow molded article of synthetic resin - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of manufacturing a hollow molded article of synthetic resin, which is advantageous when joining in homogeneity and certainty over a total length of a longitudinal direction of a joint portion, by preventing joining unevenness from being generated. <P>SOLUTION: A pair of half-hollow articles 12 which have a joint 14 at an opening edge is injection-molded in the primary molding. Each joint 14 of the pair of half-hollow articles 12 includes: an inner wall 30 located closer to an internal space 16; an outer wall 32 which is located in the opposite side with the internal space 16 across the inner wall 30; and a connecting wall 34 which connects a base of the inner wall 30 and a base of the outer wall 32. A concave part 18 is formed by the inner wall 30, the outer wall 32, and the connecting wall 34. In the secondary molding, the joints 14 of the pare of half-hollow bodies 12 are contacted, molten resin is injected to a passage 20 for joining formed in recessed parts 18 of these joints 14, and both joints 14 are joined. To demonstrate details more, the pressure of the molten resin with which the passage 20 for joining is filled is raised at the same time with the finalization of filling the passage 20 for joining with the molten resin. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a semi-hollow body for manufacturing a hollow product made of a synthetic resin manufactured by DSI (Die Slide Injection) molding.

In recent years, DSI (Die Slide Injection) molding including DRI (Die Rotation Injection) molding is known as a method for producing a hollow product made of a synthetic resin having a complicated shape.
In DSI molding, in a primary molding, a pair of semi-hollow bodies having a joint at the opening edge is injection molded. In the secondary molding, the joint portions of a pair of semi-hollow bodies immediately after molding are combined, molten resin is injected into the joint portions, the joint portions are joined together, and a molded product having an internal space is formed.
More specifically, in the secondary molding, the joining passages are formed so as to extend over the entire length of the opening edges of the pair of semi-hollow bodies by joining the joint portions of the pair of semi-hollow bodies.
In addition, when the joint portions of the pair of semi-hollow bodies are combined, an injection port for injecting the molten resin into the joint passage is formed at the joint portion located opposite to the internal space simultaneously with the formation of the joint passage. A plurality of joining passages are formed at intervals in the extending direction.
Then, the molten resin is injected into the joining passage from each injection port, and the molten resin moves in the joining passage while melting the inner wall portion of the joining passage and is filled in the joining passage. As a result, the joints are joined together to form a hollow product made of synthetic resin having an internal space.

JP 2000-309030 JP-A-2005-288808

On the other hand, although the mold used in the primary molding and the secondary molding is heated and the temperature of the semi-hollow body immediately after molding is high, the temperature of the molten resin injected into the joining passage in the secondary molding is half-hollow Higher than the temperature of.
Therefore, in the secondary molding, the temperature of the molten resin injected into the joining passage from each injection port is lowered as the joining portions of the pair of semi-hollow bodies are combined and flows through the joining passage. In particular, the temperature of the first portion of the molten resin flowing through the joining passage is the lowest.
When the temperature of the injected molten resin decreases, it becomes difficult for the molten resin to melt the inner wall portion of the joining passage, and the top of the molten resin that is injected from the adjacent injection port and flows through the joining passage collides. The parts are also difficult to weld, causing uneven bonding.
On the other hand, in order to eliminate such problems, it is conceivable to increase the temperature of the molten resin injected into the joining passage. However, when the temperature of the molten resin is increased, the amount of heat received by the inner wall portion of the joining passage where the molten resin injected from each injection port collides increases. For this reason, the injected molten resin melts the inner wall portion of the joining passage facing the injection port, penetrates the inner wall portion, and causes a problem that the molten resin leaks into the internal space.
For this reason, the conventional DSI molding tends to cause uneven bonding along the longitudinal direction of the joint, and is disadvantageous in reliably and uniformly joining the entire length in the longitudinal direction of the joint.
The present invention has been devised in view of the above circumstances, and an object of the present invention is to prevent the occurrence of unevenness in bonding and is an advantageous synthetic resin for uniformly bonding over the entire length in the longitudinal direction of the bonded portion. Another object of the present invention is to provide a method for producing a hollow molded product.

  In order to achieve the above object, the present invention comprises a pair of semi-hollow bodies having joints at the opening edges, the joints of the pair of semi-hollow bodies have recesses, and the joints are combined. By the manufacturing method of the synthetic resin hollow molded article formed by forming a joining passage by the concave portions over the entire length of the opening edge and injecting molten resin into the joining passage. A method for producing a hollow molded article made of synthetic resin in which the pressure of the molten resin filled in the bonding passage is increased simultaneously with completion of filling of the molten resin into the bonding passage.

  In the present invention, simultaneously with the completion of the filling of the molten resin into the bonding passage, the pressure of the molten resin filled in the bonding passage is increased to forcibly weld the bonded portion with the molten resin.

(A) is the perspective view which fractured | ruptured some hollow molded articles, (B) is the expansion perspective view of a junction part. In the explanatory diagram of the specific example 1, (A) is a cross-sectional view at the time of injection and filling of the molten resin into the joining passage, (B) is a disconnection of the joining passage simultaneously with completion of filling of the molten resin into the joining passage. It is sectional drawing of the state which reduced the area. In the explanatory diagram of the specific example 2, (A) is a cross-sectional view at the time of injection and filling of the molten resin into the joining passage, (B) is a disconnection of the joining passage at the same time as filling of the molten resin into the joining passage is completed. It is sectional drawing of the state which reduced the area. It is a perspective view of the hollow molded article used as the test article. It is a figure which shows a test result.

Hereinafter, embodiments of the manufacturing method of the present invention will be described with reference to the drawings.
The present invention is applied to a hollow molded product made of synthetic resin molded by DSI molding, and the shape of the hollow molded product is variously provided from a complicated shape to a simple shape, Although contemplated, the present invention is applicable to all of them.
As shown in FIG. 1 (A), the hollow molded article 10 is composed of a pair of semi-hollow bodies 12 having a joint 14 at the opening edge.
By joining the joint portions 14 of the pair of semi-hollow bodies 12, an internal space 16 is formed inside them.
The joints 14 of the pair of semi-hollow bodies 12 have recesses 18, and by joining the joints 14, the joints 20 are formed by the recesses 18 over the entire length of the opening edge.
In addition, when the joining portions 14 are combined, the injection port 22 that injects the molten resin into the joining passage 20 at the place of the joining portion 14 located opposite to the internal space 16 simultaneously with the formation of the joining passage 20. Are formed at intervals in the extending direction of the joining passage 20.
The molten resin is injected from the mold gate 24 through the injection port 22 into the bonding passage 20, whereby the bonding portion 14 is bonded, and the hollow molded article 10 made of synthetic resin is configured.
In FIG. 1, reference numeral 26 indicates a molten resin injected and filled in the bonding passage 20.

Next, the case where the hollow molded article 10 is manufactured by DSI molding will be described in the order of the steps.
In the primary molding, a pair of semi-hollow bodies 12 having joints 14 at the opening edges are injection molded.
As shown in FIG. 1B, each joint 14 of the pair of semi-hollow bodies 12 includes an inner wall 30 located near the inner space 16, and an outer wall facing the inner wall 30 and located on the opposite side of the inner space 16. 32, and a connection wall 34 that connects the base portion of the inner wall 30 and the base portion of the outer wall 32.
The recess 18 is formed by the inner wall 30, the outer wall 32, and the connection wall 34.

In the secondary molding, the joint portions 14 of the pair of semi-hollow bodies 12 are combined, and the molten resin is injected into the joint passage 20 formed by the concave portions 18 of the joint portions 14 to join the joint portions 14 together.
More specifically, the pressure of the molten resin filled in the bonding passage 20 is increased simultaneously with the completion of the filling of the molten resin into the bonding passage 20.
In the present embodiment, the pressure of the molten resin, which is performed simultaneously with the completion of filling of the molten resin into the bonding passage 20, is performed by reducing the cross-sectional area of the bonding passage 20 over the entire length of the bonding passage 20. ing.

Simultaneously with the completion of the filling of the molten resin into the bonding passage 20, the temperature of the molten resin injected into the bonding passage 20 from each injection port 22 is increased by increasing the pressure of the molten resin filled in the bonding passage 20. Even if it decreases as it flows through the joining passage 20, the molten resin and the inner wall 30 of the joining passage 20 are reliably welded. It is considered that this is because the molten resin and the inner wall 30 of the joining passage 20 are pressed with a large force, and the welding is forcibly performed.
Further, even if the temperature of the leading portion of the molten resin that is injected from the adjacent injection port 22 and flows through the joining passage 20 is the lowest, the leading portions of the colliding molten resin are reliably welded to each other. . It is considered that this is because the leading portions of the molten resin are pressed against each other with a large force, and the welding is forcibly performed.
Therefore, it is advantageous for preventing the occurrence of unevenness of joining and joining the joint portions 14 of the pair of semi-hollow bodies 12 uniformly and reliably over the entire length of the joint portions 14 in the longitudinal direction.

Next, a first specific example of a configuration in which the cross-sectional area of the joining passage 20 is reduced over the entire length of the joining passage 20 in order to increase the pressure of the molten resin will be described with reference to FIG.
As shown in FIG. 2A, the joint portion 14 of the pair of semi-hollow bodies 12 includes an inner wall 30 positioned closer to the inner space 16, and an outer wall 32 facing the inner wall 30 and positioned on the opposite side of the inner space 16. And a connection wall 34 that connects the base portion of the inner wall 30 and the base portion of the outer wall 32.
The recess 18 is formed by the inner wall 30, the outer wall 32, and the connection wall 34.
By joining the joint portions 14 of the pair of semi-hollow bodies 12, the front portions of the inner walls 30 of the respective joint portions 14 and the front portions of the outer walls 32 are brought together, and a joining passage 20 is formed between the joint portions 14. The
Further, an injection port 22 (see FIG. 1) for injecting the molten resin into the bonding passage 20 is spaced apart in the extending direction of the bonding passage 20 at a position of the bonding portion 14 positioned opposite to the internal space 16. A plurality are formed.
An inclined surface that is inclined with respect to the direction in which each joint portion 14 is fitted to the location of the front portion of the inner wall 30 of each joint portion 14 and the location of the front portion of the outer wall 32 of each joint portion 14 that are located on the side of the joining passage 20. 30A and 40A are formed, respectively.
In addition, in the state where the inclined surface 30A and the inclined surface 40A of each joint portion 14 are combined with each other at the tip portion of one inner wall 30 positioned opposite to the bonding passage 20 and the one outer wall 32, Notches are provided so that gaps S <b> 1 and S <b> 2 are generated between the front portions of the inner wall 30 and the front portion of the outer wall 32 in the mating direction.

The injection and filling of the molten resin from each injection port 22 into the bonding passage 20 are performed in a state where the inclined surface 30A of the inner wall 30 of each joint portion 14 is combined and the inclined surface 40A of the outer wall 32 of each joint portion 14 is combined. To do.
In FIG. 2, reference numeral 26 indicates a molten resin injected and filled in the bonding passage 20.
Simultaneously with the completion of the filling of the molten resin 26 into the bonding passage 20, as shown in FIG. 2B, the pressure of the molten resin filled in the bonding passage 20 is reduced by reducing the cross-sectional area of the bonding passage 20. To increase.
The reduction of the cross-sectional area of the joining passage 20 is achieved by sliding the inclined surface 30A of the inner wall 30 of each joint portion 14 while maintaining the contact state and the inclined surface 40A of the outer wall 32 of each joint portion 14 being in contact therewith. This is done by sliding while maintaining the state.
The reduction of the cross-sectional area of the joining passage 20 is performed smoothly because the inclined surfaces 30A and the inclined surfaces 40A are in contact with each other.
After the cross-sectional area of the joining passage 20 is reduced, the gap S1 between the front portions of the inner wall 30 and the gap S2 between the front portions of the outer wall 32 are not blocked.

The sliding of these inclined surfaces 30A and 40A is performed by moving a pair of molds located outside the pair of semi-hollow bodies 12 in a direction to approach each other during the secondary molding.
Alternatively, it is performed by moving only the portions corresponding to the joint portions 14 of the pair of molds located outside the pair of semi-hollow bodies 12 in a direction to approach each other.
In the present embodiment, the gaps S1 and S2 are provided between the front portions of the inner wall 30 and the front portion of the outer wall 32 in a state where the inclined surfaces 30A and the inclined surfaces 40A of the joint portions 14 are combined. The cross-sectional area of the working passage 20 can be reduced more smoothly.
In this way, simultaneously with the completion of the filling of the molten resin into the bonding passage 20, the cross-sectional area of the bonding passage 20 is reduced to increase the pressure of the molten resin, thereby preventing the occurrence of uneven bonding and the longitudinal direction of the bonding portion 14. This is advantageous for assuring a uniform and uniform joining over the entire length of the.

Next, a second specific example in which the cross-sectional area of the joining passage 20 is reduced over the entire length of the joining passage 20 in order to increase the pressure of the molten resin will be described.
As shown in FIG. 3A, the recess 18 is formed by the inner wall 30, the outer wall 32, and the connection wall 34, and the joining portion 14 of the pair of semi-hollow bodies 12 is combined to form the joining passage 20. It is the same as in the first example in that it is formed and a plurality of injection ports 22 are formed.
In the second specific example, a thin-walled portion 32 </ b> A having a reduced thickness is formed at the front portion of one outer wall 32 of the pair of semi-hollow bodies 12 so as to be easily deformed.
In addition, a portion 30 </ b> B having a width narrower than the front portion of the facing inner wall 30 is formed at the front portion of the other inner wall 30 of the pair of semi-hollow bodies 12.

Injection and filling of the molten resin from each injection port 22 into the bonding passage 20 are performed by combining the tip of the inner wall 30 of the pair of semi-hollow bodies 12 and the tip of the portion 30B having a narrow width of the inner wall 30; and In this state, the tip of the thin wall portion 32A of the outer wall 12 and the tip of the outer wall 32 are combined.
Then, as shown in FIG. 3B, simultaneously with the completion of the filling of the molten resin into the bonding passage 20, the cross-sectional area of the bonding passage 20 is reduced, and the pressure of the molten resin filled in the bonding passage 20 is reduced. Increase.
The reduction of the cross-sectional area of the bonding passage 20 is performed by further pressing the tip of the inner wall 30 of the pair of semi-hollow bodies 12 and the tip of the portion 30B having the narrowed inner wall 30 to deform the tip of the inner wall 30. In addition, the tip of the thin-walled tip 32A and the tip of the outer wall 32 are further pressed to deform the tip of the outer wall 32. In the present embodiment, for example, as shown in FIG. 3B, the portion 30B with the narrowed inner wall 30 sinks into the front portion of the opposing inner wall 30, and the thin portion 32A of the outer wall 32 is crushed. Deformation is made.

The pressing between the inner wall 30 and the outer wall 32 of each joint portion 14 moves the pair of molds positioned outside the pair of semi-hollow bodies 12 in the direction of approaching each other during the secondary molding. This is done.
Alternatively, it is performed by moving only the portions corresponding to the joint portions 14 of the pair of molds located outside the pair of semi-hollow bodies 12 in a direction to approach each other.
It should be noted that the narrowed portion 30B and the thin portion 32A are not provided, and when the cross-sectional area of the joining passage 20 is reduced, the tip portions of the inner wall 30 and the tip portions of the outer wall 32 are simply pressed to deform the wall portions. However, providing at least one of the narrowed portion 30B or the thin portion 32A as described above is easy to deform and is advantageous in smoothly reducing the cross-sectional area of the joining passage 20. Become.
In this way, simultaneously with the completion of the filling of the molten resin into the bonding passage 20, the cross-sectional area of the bonding passage 20 is reduced to increase the pressure of the molten resin, thereby preventing the occurrence of uneven bonding and the longitudinal direction of the bonding portion 14. This is advantageous for assuring a uniform and uniform joining over the entire length of the.

Next, test results for the examples and comparative examples will be described.
A cylindrical hollow molded article 10 shown in FIG. 4 was manufactured from the pair of semi-hollow bodies 12 by DSI molding.
At that time, in the secondary molding, injection and filling of the molten resin into the bonding passage 20 are performed in a state in which the front part of the inner wall 30 of each joint part 14 is combined and the front part of the outer wall 32 is combined. The cross-sectional area of the joining passage 20 at that time was 100 mm ² .
In Comparative Example 1, the pressure of the molten resin filled in the bonding passage 20 was not increased, but was cooled as it was to cure the molten resin.
In Example 1, simultaneously with completion of filling of the molten resin into the bonding passage 20, one of the pair of molds positioned outside the pair of semi-hollow bodies 12 is kept stationary, and the other mold The mold was moved 0.005 mm toward one mold. By this movement, the cross-sectional area of the joining passage 20 is changed from 100 mm ² to 98.5 mm ² .

In Example 2, simultaneously with the completion of filling of the molten resin into the bonding passage 20, one of the pair of molds positioned outside the pair of semi-hollow bodies 12 is kept stationary, and the other mold is placed. The mold was moved 0.01 mm toward one mold. This movement, the cross-sectional area of the joint passage 20 became 98.0Mm ² from 100 mm ^2.
In Example 3, simultaneously with the completion of filling of the molten resin into the bonding passage 20, one of the pair of molds located outside the pair of semi-hollow bodies 12 is kept stationary, and the other mold is placed. The mold was moved 0.015 mm toward one mold. This movement, the cross-sectional area of the joint passage 20 became 97.5mm ² from 100 mm ^2.
In Example 4, simultaneously with the completion of filling of the molten resin into the bonding passage 20, one of the pair of molds located outside the pair of semi-hollow bodies 12 is stationary and the other mold is fixed. The mold was moved 0.02 mm toward one mold. This movement, the cross-sectional area of the joint passage 20 became 97.0Mm ² from 100 mm ^2.

In the fifth embodiment, at the same time when the molten resin is filled into the bonding passage 20, one of the pair of molds located outside the pair of semi-hollow bodies 12 is kept stationary, and the other mold is placed. The mold was moved 0.025 mm toward one mold. This movement, the cross-sectional area of the joint passage 20 became 96.5Mm ² from 100 mm ^2.
In Example 6, simultaneously with the completion of filling of the molten resin into the bonding passage 20, one of the pair of molds located outside the pair of semi-hollow bodies 12 is kept stationary, and the other mold The mold was moved 0.03 mm toward one mold. This movement, the cross-sectional area of the joint passage 20 became 96.0Mm ² from 100 mm ^2.
In Example 7, simultaneously with the completion of filling of the molten resin into the bonding passage 20, one of the pair of molds located outside the pair of semi-hollow bodies 12 is kept stationary, and the other mold The mold was moved 0.035 mm toward one mold. This movement, the cross-sectional area of the joint passage 20 became 95.5Mm ² from 100 mm ^2.

Five hollow molded articles 10 molded in Comparative Example 1 were prepared.
And the pressure to the internal space 16 of those hollow molded articles 10 was raised, and the pressure when the junction part 14 was destroyed was measured. The highest pressure at this time was 100 kg / cm ² .
Five hollow molded articles 10 molded in Examples 1 to 7 were prepared, and 100 kg / cm ² pressure was applied to each internal space 16.
In Example 1, there were two of the five hollow molded articles 10 in which the joint portion 14 was broken.
In Examples 2 to 6, none of the five hollow molded articles 10 had the joint 14 destroyed.
In Example 7, there were two of the five hollow molded articles 10 in which the joint portion 14 was destroyed.
The test results of Examples 1 to 7 are shown in FIG.
In FIG. 5, the hollow molded product 10 that was not destroyed is indicated by “◯”, and the broken hollow molded product 10 is indicated by “X”.
In Comparative Example 1, when the pressure of 100 kg / cm ^{2 is} applied to the internal space 16 of the five hollow molded products 10, the joint portions 14 of all the hollow molded products 10 are destroyed, and therefore, FIG. It was shown as Comparative Example 1 together with Examples 1-7.

As is apparent from the test results of Examples 1 to 7 shown in FIG. 5, Comparative Example 1 does not increase the pressure of the molten resin when the pressure of the molten resin is increased simultaneously with the completion of the filling of the molten resin into the bonding passage 20. As compared with the above, it is advantageous in reliably welding the joint portions 14 to each other by the molten resin injected into the joining passage 20.
However, in the pressure increase of the molten resin according to the first embodiment performed simultaneously with the completion of filling of the molten resin into the bonding passage 20, the temperature of the molten resin injected from each injection port 22 into the bonding passage 20 is It is considered that the molten resin and the inner wall 30 of the joining passage 20 were not surely welded to each other as the fluid flowed. In addition, the temperature of the leading portion of the molten resin injected from the adjacent injection port 22 and flowing through the joining passage 20 is the lowest, and the leading portions of the colliding molten resin are not reliably welded to each other. It is thought that it occurred.
Further, in the pressure increase of the molten resin according to the seventh embodiment performed simultaneously with the completion of the filling of the molten resin into the joining passage 20, the deformation amount between the front portions of the inner wall 30 is large, and the deformation amount between the front portions of the outer wall 32. Therefore, when the mold is opened and the hollow molded product 10 is taken out, the front portions of the inner wall 30 are deformed in a direction away from each other due to internal residual stress, and the front portions of the outer wall 32 are separated from each other. It is thought that the deformation | transformation to the direction and what joined the junction part 14 became inadequate occurred.
On the other hand, in Examples 2 to 6, it is considered that the joints 14 were reliably welded to each other by the molten resin due to the pressure increase of the molten resin.
Therefore, the reduction of the cross-sectional area of the bonding passage 20 is such that the cross-sectional area of the bonding passage 20 is 96 when the cross-sectional area of the bonding passage 20 at the completion of filling of the molten resin into the bonding passage 20 is 100. It is preferable to be carried out in the range of 98 to 98.

In the above embodiment, the case where the cross-sectional area of the joining passage 20 is reduced by sliding the inclined surfaces 30A and 40A or by deforming the front portion of the inner wall 30 or the outer wall 32 has been described. The inner wall 30 and the outer wall 32 may be slid or deformed as follows.
That is, the connecting wall 34 is deformed over the entire length in the extending direction of the joining passage 20 to the joining passage 20 side to reduce the cross-sectional area of the joining passage 20, and the molten resin filled in the joining passage 20 is made. The pressure may be increased over the entire length of the joining passage 20.
Alternatively, the molten resin filled in the joining passage 20 is formed by deforming a plurality of locations spaced in the extending direction of the joining passage 20 toward the joining passage 20 to reduce the cross-sectional area of the joining passage 20. The pressure may be increased over the entire length of the joining passage 20.

  DESCRIPTION OF SYMBOLS 10 ... Hollow molded article, 12 ... Semi-hollow body, 14 ... Joining part, 16 ... Internal space, 18 ... Recessed part, 20 ... Passage for joining, 30 ... Inner wall, 32 ... Outer wall, 34 ... ... connection wall.

Claims (7)

It consists of a pair of semi-hollow bodies having a joint portion at the opening edge, and the joint portions of the pair of semi-hollow bodies have a concave portion, and by joining the joint portions, the concave portions are joined over the entire length of the opening edge. A method for producing a hollow molded article made of a synthetic resin, wherein a joint passage is formed, and the joining portion is joined by injecting molten resin into the joining passage.
Simultaneously with the completion of filling of the molten resin into the bonding passage, the pressure of the molten resin filled in the bonding passage is increased.
A method for producing a hollow molded product made of synthetic resin.   The pressure increase of the molten resin performed simultaneously with completion of filling of the molten resin into the bonding passage is performed by reducing the cross-sectional area of the bonding passage over the entire length of the bonding passage. Of manufacturing hollow molded article made of synthetic resin.   The reduction of the cross-sectional area of the joining passage is such that the cross-sectional area of the joining passage is 96 or more and 98 when the cross-sectional area of the joining passage at the completion of filling of the molten resin into the joining passage is 100. The method for producing a hollow molded article made of a synthetic resin according to claim 2, which is carried out within the following range. An internal space is formed inside the pair of semi-hollow bodies by combining the joints of the pair of semi-hollow bodies,
Each of the joint portions includes an inner wall located closer to the inner space, an outer wall facing the inner wall and located on the opposite side of the inner space, and a connecting wall connecting the base portion of the inner wall and the base portion of the outer wall. The recesses are formed by the inner wall, the outer wall, and the connection wall,
An inclined surface that is inclined with respect to the direction in which the joint portions are combined is formed at the tip portion of the inner wall of each joint portion and the tip portion of the outer wall of each joint portion,
Injection and filling of the molten resin into the bonding passage is performed in a state where the inclined surfaces of the inner walls of the joints are combined and the inclined surfaces of the outer walls of the joints are combined.
To reduce the cross-sectional area of the joining passage, the inclined surface of the inner wall of each joint is slid while maintaining its contact state, and the inclined surface of the outer wall of each joint is slid while maintaining its contact state. To be done,
A method for producing a hollow molded product made of a synthetic resin according to claim 2. An internal space is formed inside the pair of semi-hollow bodies by combining the joints of the pair of semi-hollow bodies,
Each of the joint portions includes an inner wall located closer to the inner space, an outer wall facing the inner wall and located on the opposite side of the inner space, and a connecting wall connecting the base portion of the inner wall and the base portion of the outer wall. The recesses are formed by the inner wall, the outer wall, and the connection wall,
Injection and filling of the molten resin into the bonding passage is performed in a state where the front portions of the inner walls of the joint portions are combined and the front portions of the outer walls of the joint portions are combined,
The reduction of the cross-sectional area of the joining passage is performed by further pressing and deforming the tip portions of the inner walls of the joint portions, and further pressing and deforming the tip portions of the outer walls of the joint portions.
A method for producing a hollow molded product made of a synthetic resin according to claim 2. Of the pair of semi-hollow bodies, the tip of the outer wall of the joining part of one half-hollow body is joined to the tip of the outer wall of the other half-hollow body during injection and filling of the molten resin into the joining passage. A thin part with a reduced thickness is formed at the location where
When the cross-sectional area of the bonding passage is reduced, when the front portions of the outer walls of each bonding portion are further pressed against each other, the thin-walled portion deforms.
A method for producing a hollow molded product made of a synthetic resin according to claim 5.   The increase in the pressure of the molten resin, which is performed simultaneously with the completion of filling of the molten resin into the bonding passage, is caused by the cross-sectional area of the bonding passage at a plurality of positions spaced in the extending direction of the bonding passage. The method for producing a hollow molded article made of a synthetic resin according to claim 1, which is carried out by reducing the size.

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