JP7428888B2 - Method for manufacturing molded bodies - Google Patents

Description

The present invention relates to a method for manufacturing a molded article.

In blow molding, a molded article is manufactured by blowing air into the parison with a cylindrical parison sandwiched between split molds.

In Patent Document 1, after pinching the parison with a pinch device provided below the split mold, pre-blowing is performed by blowing air into the parison, and then the split mold is closed and main blowing is performed.

Japanese Patent Application Publication No. 6-8313

The part of the parison outside the cavity of the split mold becomes burr that is not included in the final product. The greater the ratio of burrs to the weight of the parison (hereinafter referred to as "burr ratio"), the worse the utilization efficiency of the resin constituting the parison. The higher the burr ratio, the higher the manufacturing cost tends to be, and it is desired to reduce the burr ratio.

The present invention has been made in view of these circumstances, and provides a method for manufacturing a molded article that can reduce the burr ratio.

According to the present invention, there is provided a method for manufacturing a molded body using first and second molds, which comprises an extrusion step, a pinch step, a pre-blowing step, and a molding step, and in the extrusion step, Extruding the molten resin to form a cylindrical parison and extruding it between the first and second molds in an open state, and in the pinching step, in the region between the vertical center and the lower end of the first mold, A pinch part pinches the parison and forms a closing part that closes the lower side of the parison, and in the pre-blow step, air is blown into the parison from a pre-blow nozzle provided in the extrusion head, and in the forming step, , a method is provided for forming the parison by closing first and second molds.

The inventor conducted extensive studies to reduce the burr ratio, and found that as the degree of drawdown of the parison increases, the weight of the resin located below the cavity increases, resulting in an increase in the burr ratio. noticed. After conducting intensive studies to suppress drawdown, we found that when performing pre-blowing by pinching in the area between the vertical center and the bottom end of the first mold, when pinching outside the above area, In comparison, it was found that the degree of drawdown of the parison can be reduced. Therefore, according to the present invention, the burr ratio can be reduced.

Various embodiments of the present invention will be illustrated below. The embodiments shown below can be combined with each other.
Preferably, in the method described above, the first and second molds start closing operations before the closing portion reaches the lower end of the first mold.
Preferably, in the method described above, in the pinching step, the pinching section performs a closing operation at a timing set from a point in time when a sensor placed at a higher position than the pinching section detects the parison. This is the way to start.
Preferably, the method described above is a method in which the pinch portion moves while sandwiching the parison.
Preferably, the method as described above, wherein the parison is a foamed parison.

An example of a molding machine 1 that can be used in the method for manufacturing a molded body according to an embodiment of the present invention is shown. 2 is an enlarged view of the vicinity of molds 21 and 22 in FIG. 1. FIG. A state after the parison 23 is further pushed out from the state shown in FIG. 2 and then pinched between the pinch parts 29 is shown. The state after the pinch portion 29 is removed from the state shown in FIG. 3 and the parison 23 is further pushed out while pre-blowing is shown. The parison 23 is further extruded from the state shown in FIG. 4 while pre-blowing, and then the molds 21 and 22 are closed to perform blow molding. It is a typical graph which shows the relationship between the pinch position P (P/H) with respect to the height H of the metal mold|die 21, and the degree of drawdown.

Embodiments of the present invention will be described below. Various features shown in the embodiments described below can be combined with each other. Further, the invention is established independently for each characteristic matter.

1. Configuration of Molding Machine 1 First, a molding machine 1 that can be used to carry out a method for manufacturing a molded article according to an embodiment of the present invention will be described with reference to FIGS. 1 to 3. The molding machine 1 includes a resin supply device 2 , an extrusion head 18 , first and second split molds 21 and 22 , a pinch section 29 , and a sensor 30 . The resin supply device 2 includes a hopper 12, an extruder 13, an injector 16, and an accumulator 17. The extruder 13 and the accumulator 17 are connected via a connecting pipe 25. The accumulator 17 and the extrusion head 18 are connected via a connecting pipe 27.
Each configuration will be explained in detail below.

<Hopper 12, extruder 13>
The hopper 12 is used to charge the raw resin 11 into the cylinder 13a of the extruder 13. Although the form of the raw resin 11 is not particularly limited, it is usually in the form of pellets. The raw resin 11 is, for example, a thermoplastic resin such as polyolefin, and examples of the polyolefin include low density polyethylene, linear low density polyethylene, high density polyethylene, polypropylene, ethylene-propylene copolymer, and mixtures thereof. The raw resin 11 is charged into the cylinder 13a from the hopper 12, and then heated and melted into a molten resin in the cylinder 13a. Furthermore, the material is conveyed toward the tip of the cylinder 13a by rotation of a screw disposed within the cylinder 13a. The screw is disposed within the cylinder 13a, and its rotation transports the molten resin while kneading it.

<Injector 16>
The cylinder 13a is provided with an injector 16 for injecting a foaming agent into the cylinder 13a. When the raw resin 11 is not foamed, the injector 16 can be omitted. The foaming agent injected from the injector 16 includes physical foaming agents, chemical foaming agents, and mixtures thereof, but physical foaming agents are preferable. Examples of the physical blowing agent include carbon dioxide gas and nitrogen gas. Examples of chemical blowing agents include those that generate carbon dioxide gas through a chemical reaction between an acid (eg, citric acid or its salt) and a base (eg, baking soda). The chemical foaming agent may be introduced from the hopper 12 instead of being injected from the injector 16.

<Accumulator 17, extrusion head 18>
The molten resin 11a with or without the foaming agent added is extruded from the resin extrusion port of the cylinder 13a and injected into the accumulator 17 through the connecting pipe 25. The accumulator 17 includes a cylinder 17a and a piston 17b that is slidable inside the cylinder 17a, and the molten resin 11a can be stored in the cylinder 17a. After a predetermined amount of molten resin 11a is stored in the cylinder 17a, by moving the piston 17b, the molten resin 11a is pushed out through the annular slit provided in the extrusion head 18 through the connecting pipe 27 and is made to hang down to form a cylindrical shape. A parison 23 is formed. The extrusion head 18 is provided with a pre-blow nozzle 28, and air can be blown into the parison 23 from the pre-blow nozzle 28 before the molds 21 and 22 are closed. The pre-blow nozzle 28 is provided so as to protrude downward from an area inside the annular slit of the extrusion head 18. The amount of protrusion of the pre-blow nozzle 28 from the lower end of the extrusion head 18 may be fixed or adjustable.

<Molds 21, 22, pinch portion 29, sensor 30>
The parison 23 is guided between the molds 21 and 22 in an open state. By molding the parison 23 using the molds 21 and 22, a molded body is obtained.

The molds 21 and 22 include cavity surfaces 21a and 22a and pinch-off portions 21b and 22b surrounding the cavity surfaces 21a and 22a. When the molds 21 and 22 are closed, the cavity surfaces 21a and 22a are brought together to form a cavity corresponding to the desired molded product.

The molding method using the molds 21 and 22 is not particularly limited, and may be blow molding in which air is blown into the cavities of the molds 21 and 22. Vacuum forming may be used to form the parison 23 by reducing the pressure inside the cavity, or a combination thereof may be used. When the molten resin contains a foaming agent, the parison 23 becomes a foamed parison, and the molded article becomes a foamed molded article.

As shown in FIGS. 2 and 3, the pinch portion 29 has a closing portion 23a that closes the lower side of the parison 23 with the parison 23 in between in the region R between the vertical center C and the lower end B of the mold 21. It is configured so that it can be formed. By pinching the parison 23 with the pinch portions 29, a sealed space 23s can be formed in the parison 23 before the molds 21 and 22 are clamped. The pinch part 29 includes a pair of pinch members 29a, and can be opened and closed by changing the distance between the pair of pinch members 29a. The pinch portion 29 may be separated from the parison 23 immediately after forming the closing portion 23a, or may be moved while sandwiching the parison 23.

When the pinch parts 29 sandwich the parison 23, the weight of the parison 23 is supported by the pinch parts 29. Therefore, drawdown of the parison 23 can be suppressed by moving the pinch part 29 downward in conjunction with extrusion of the parison 23 with the pinch part 29 sandwiching the parison 23. In addition, with the pinch part 29 sandwiching the parison 23, the pinch part 29 is moved in a direction perpendicular to the paper surface of FIG. It may also be moved in the fold width direction. In this case, shapeability can be improved by deforming the parison 23 so as to approximate the shape of the cavities of the molds 21 and 22.

The pinch part 29 is arranged between the molds 21 and 22 in an open state when pinching is performed. On the other hand, before closing the molds 21 and 22, the pinch part 29 is placed in the area between the molds 21 and 22 so that the pinch part 29 is not pinched between the molds 21 and 22. evacuate outside. The pinch portion 29 may be retracted by moving below the molds 21 and 22, or may be retracted by moving in a direction perpendicular to the paper plane of FIG.

The sensor 30 is configured to be able to detect the parison 23. The sensor 30 is arranged at a higher position than the pinch part 29. In one example, the timing of the operation of the pinch section 29 to pinch the parison 23 can be controlled starting from the point in time when the sensor 30 detects that the lower end of the parison 23 has reached a predetermined height position. The pinch part 29 may start the closing operation immediately when the sensor 30 detects the lower end of the parison 23, or the pinch part 29 starts the closing operation after a predetermined time has elapsed from the time when the sensor 30 detects the lower end of the parison 23. You may. The sensor 30 may be configured to move together with the pinch section 29 as in this embodiment, or may be configured to be movable by a drive mechanism separate from the pinch section 29.

2. Method for Manufacturing a Molded Body A method for manufacturing a molded body according to an embodiment of the present invention includes an extrusion process, a pinch process, a pre-blowing process, and a molding process.

<Extrusion process>
As shown in FIG. 2, in the extrusion process, the molten resin is extruded to form a cylindrical parison 23, which is extruded between open molds 21 and 22.

<Pinch process>
As shown in FIG. 3, in the pinching process, the pinching part 29 pinches the parison 23 (that is, pinches it) in the region R between the vertical center C and the lower end B of the mold 21 and presses it under the parison 23. A closing portion 23a that closes the side is formed. As a result, a sealed space 23s is formed within the parison 23.

It is preferable that the pinch section 29 starts its closing operation at a set timing starting from the point in time when the sensor 30 disposed at a higher position than the pinch section 29 detects the parison 23 . By controlling the start timing of the closing operation of the pinch portion 29 in this manner, even if there is variation in the extrusion speed of the parison 23, it is possible to suppress variation in the position where the closing portion 23a is formed.

If the length of the mold 21 in the vertical direction is H, and the distance from the lower end B of the mold 21 to the position where the pinch part 29 pinches the parison 23 (hereinafter referred to as the "pinch position") is P, then P/H is: 0 to 0.5, preferably 0.05 to 0.3, specifically, for example, 0, 0.05, 0.1, 0.2, 0.3, 0.4, 0.5. Yes, it may be within the range between any two of the numerical values exemplified here.

If the pinch position is too high, the time T1 for pre-blowing while pushing out the parison 23 after pinching becomes longer. As the time T1 becomes longer, the drawdown progresses at an accelerated rate, so if the pinch position is too high, the drawdown of the parison 23 tends to become noticeable (Factor 1).

On the other hand, if the pinch position is too low, the timing of starting the process of expanding the parison 23 by pre-blowing will be delayed by that amount, and as a result, the time T2 from the start of extrusion of the parison 23 to the completion of mold closing will become longer. As the time T2 becomes longer, the drawdown progresses more rapidly, so if the pinch position is too high, the drawdown of the parison 23 tends to become noticeable (Factor 2).

As shown in Figure 6, when the pinch position is too high (P/H > 0.5), the influence of factor 2 is small because T2 is short, but the influence of factor 1 is very large because T1 is long. This increases the degree of drawdown. On the other hand, if the pinch position is too low (P/H < 0), the effect of factor 1 is small because T1 is short, but the effect of factor 2 is very large because T2 is long, and therefore the degree of drawdown is growing. When the pinch position is within region R (when P/H = 0 to 0.5), both T1 and T2 are medium values, so the effects of factor 1 and factor 2 are medium. As a result, drawdown becomes less noticeable. Therefore, when the pinch position is within the region R, the degree of drawdown tends to be small.

Drawdown occurs whether the parison 23 is a foamed parison or a non-foamed parison, but the degree of drawdown tends to be large in a foamed parison, so the present invention is applied when the parison 23 is a foamed parison. The technical significance of this is remarkable. When the molded body is elongated like a duct, the stability of the product weight is particularly low, so the technical significance of applying the present invention is also significant in this case as well.

<Pre-blow process>
As shown in FIGS. 3 and 4, in the pre-blowing step, air is blown into the parison 23 (that is, the sealed space 23s) from the pre-blowing nozzle 28 provided in the extrusion head 18 (that is, pre-blowing is performed). This allows the parison 23 to expand. Pre-blow may be started before forming the closed portion 23a, or may be started after the closed portion 23a is formed. Preferably, the pre-blowing is stopped after extrusion of the parison 23 is completed (that is, the movement of the closing portion 23a is stopped). This is because if the pre-blowing is stopped before the extrusion of the parison 23 is completed, the pressure inside the sealed space 23s will be reduced and the parison 23 will deflate.

In this embodiment, since pre-blowing is started before extrusion of the parison 23 is completed, pre-blowing is performed while the closing part 23a moves downward. For this reason, if a pre-blow nozzle is inserted from the closed part 23a side to perform pre-blow, it is necessary to move the pre-blow nozzle in synchronization with the movement of the closed part 23a, which makes the control complicated. In this embodiment, since pre-blowing is performed using the pre-blowing nozzle 28 provided on the extrusion head 18, there is no need to move the pre-blowing nozzle 28 during pre-blowing, and the control is simple. In addition, particularly when the parison 23 is a foamed parison, there is a phenomenon in which the parison 23 becomes folded at a position close to the extrusion head 18 and the inner surfaces of the parison 23 stick together (hereinafter referred to as "creased flesh phenomenon"). ) is likely to occur, but when pre-blowing is performed from the pre-blow nozzle 28 provided in the extrusion head 18, the occurrence of the crease phenomenon is effectively suppressed.

The timing at which the pinch portion 29 separates from the parison 23 is before the start of pre-blow, during pre-blow, or
It may be done either after the pre-blow is completed.

<Molding process>
As shown in FIGS. 4 and 5, in the molding process, the molds 21 and 22 are closed and the parison 23 is molded. At this time, a molded body 23m is formed in the molds 21 and 22, an upper burr part 23t is formed on the upper side of the molds 21 and 22, and a lower burr part 23b is formed on the lower side of the molds 21 and 22. is formed. According to the present embodiment, since the drawdown of the parison 23 is suppressed, the weight of the lower burr portion 23b is reduced, and as a result, the burr ratio is reduced.

It is preferable that the molds 21 and 22 start the closing operation before the closing portion 23a (preferably the lower end of the parison 23) reaches the lower end of the mold 21. As a result, the time T2 from the start of extrusion of the parison 23 to the completion of mold closing can be shortened, and drawdown and cycle time can be reduced.

The start timing of the closing operation of the molds 21 and 22 can be set, for example, at the point in time when the pinch portion 29 starts to separate from the area between the molds 21 and 22. This can prevent the molds 21 and 22 from pinching the pinch portion 29. For example, the closing operation of the molds 21 and 22 can be started after a predetermined waiting time has elapsed from the time when the pinch portion 29 starts to detach. The waiting time can be set depending on the positions of the molds 21 and 22 and the mold closing speeds of the molds 21 and 22.

<Post-process>
In the post-process, the molded body 23m with the upper burr part 23t and the lower burr part 23b is taken out from the molds 21 and 22, and the upper burr part 23t and the lower burr part 23b are removed from the molded body 23m. In this way, a desired molded body 23m can be obtained. To take out the molded body 23m, for example, with the molds 21 and 22 closed, the upper burr part 23t is held between the pinch parts 29, and after opening the molds 21 and 22 in this state, the pinch parts 29 are held in place as shown in FIG. This can be done by moving the image in a direction perpendicular to the plane of the paper. In other words, the pinch portion 29 can be used to take out the molded body 23m.

1: Molding machine 2: Resin supply device 11: Raw resin 11a: Molten resin 12: Hopper 13: Extruder 13a: Cylinder 16: Injector 17: Accumulator 17a: Cylinder 17b: Piston 18: Extrusion head 21: First divided mold 21a: Cavity surface 21b: Pinch-off section 22: Second split mold 22a: Cavity surface 22b: Pinch-off section 23: Parison 23a: Closed section 23b: Lower burr section 23m: Molded body 23s: Sealed space 23t: Upper burr section 25: Connecting pipe 27 : Connecting pipe 28 : Pre-blow nozzle 29 : Pinch part 29a : Pinch member 30 : Sensor B : Lower end C : Center R : Region

Claims (5)

A method for manufacturing a molded body using first and second molds, the method comprising:
Equipped with an extrusion process, a pinch process, a pre-blow process, and a molding process,
In the extrusion step, extruding the molten resin from an extrusion head to form a cylindrical parison and extruding it between first and second molds in an open state;
In the pinch step, the pinch part forms a closing part that sandwiches the parison and closes the lower side of the parison in a region between the vertical center and the lower end of the first mold,
In the pre-blow step, air is blown into the parison from a pre-blow nozzle provided in the extrusion head,
In the molding step, the parison is molded by closing the first and second molds ,
The method includes retracting the pinch portion out of an area between the first and second molds before closing the first and second molds . A method for manufacturing a molded body using first and second molds, the method comprising:
Equipped with an extrusion process, a pinch process, a pre-blow process, and a molding process,
In the extrusion step, extruding the molten resin from an extrusion head to form a cylindrical parison and extruding it between first and second molds in an open state;
In the pinch step, the pinch part forms a closing part that sandwiches the parison and closes the lower side of the parison in a region between the vertical center and the lower end of the first mold,
In the pre-blow step, air is blown into the parison from a pre-blow nozzle provided in the extrusion head,
In the molding step, the parison is molded by closing the first and second molds,
In the pinching step, the pinching section starts a closing operation at a set timing starting from a point in time when a sensor placed higher than the pinching section detects the parison. A method for manufacturing a molded body using first and second molds, the method comprising:
Equipped with an extrusion process, a pinch process, a pre-blow process, and a molding process,
In the extrusion step, extruding the molten resin from an extrusion head to form a cylindrical parison and extruding it between first and second molds in an open state;
In the pinch step, the pinch part forms a closing part that sandwiches the parison and closes the lower side of the parison in a region between the vertical center and the lower end of the first mold,
In the pre-blow step, air is blown into the parison from a pre-blow nozzle provided in the extrusion head,
In the molding step, the parison is molded by closing the first and second molds,
A method in which the pinch portion moves while sandwiching the parison. The method according to any one of claims 1 to 3 ,
The first and second molds start a closing operation before the closure reaches the lower end of the first mold. The method according to any one of claims 1 to 4,
The method, wherein the parison is a foam parison.