JPH0911325A - Blow molding method - Google Patents

Abstract

PURPOSE: To blow-mold a preform in an optimum temperature condition and to heat the inside surface of the preform to a specified temperature by decreasing the temperature difference between the inside surface and the outside surface and making the temperature of the inside surface higher than that of the outside surface. CONSTITUTION: In a blow molding machine 1, the first, second, and third cooling mechanisms 40, 50, 60 are fixed at the outlets of an initial heating station 4, a middle heating station 5, and a final heating station 6, respectively. When heating is stopped, since air is ejected from air blowout openings 41, 51, 61 to the outside surface PA of a preform P, the temperature of the inside surface PB with a high blow ratio becomes higher than that of the outside surface PA.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to PET (polyethylene terephthalate) bottles and PP (polypropylene).
The present invention relates to a blow molding method suitable for molding a manufactured bottle or the like. More specifically, the present invention relates to a heating and cooling technique for bringing a preform into a temperature state suitable for blow molding.

[0002]

2. Description of the Related Art Most of hollow molded articles such as plastic bottles are manufactured by blow molding a bottomed cylindrical preform made of a thermoplastic resin formed by injection molding. Among such blow molding methods, in the so-called cold parison type blow molding method, the preform is put into the blow molding apparatus at room temperature, and therefore, in this molding apparatus, before the blow molding in the blow molding die. It is necessary to heat the preform to a predetermined temperature. In this heating step, radiant heating is performed toward the outer surface of the preform.
Here, the heating of the preform is set so that the bottle or the like after molding can be molded so as to have a uniform wall thickness distribution or a predetermined wall thickness distribution, or a condition in which it can be molded in a highly oriented crystal state. To be done. Further, when manufacturing a PET bottle or the like, the heating conditions of the preform are set so that the whole is transparent.

[0003]

In the conventional blow molding method, when heating the preform, radiant heating is performed from the outer surface of the preform, so that the outer surface is heated faster. Therefore, as shown in FIG. 8, the heating period t
21, of course, the period t22 after the heating is completed.
In the above, the temperature T _PA of the outer surface of the preform is higher than the temperature T _{PB of the} inner surface, and the temperature distribution in the thickness direction of the preform is not appropriate, so that the preform cannot be uniformly blow-molded. There is a point. That is, in FIG. 9, as schematically showing how a bottle is molded from a preform, a preform P having an outer diameter dimension of 28 mm and a wall thickness of 4 mm is used to form an outer diameter dimension of 80 mm and a wall thickness of 0.3 mm. When blowing and molding bottle B of
The blow ratio of the outer surface PA is about 2.9 times, and the inner surface P is
Since the blow ratio of B is about 4.0, it is necessary to make the temperature of the inner surface PB of the preform having a high blow ratio higher than that of the outer surface PA in order to perform proper blow molding. The distribution cannot be achieved simply by heating from the outer surface as in conventional heating methods.

Further, even if the preform is softened by being heated, it cannot be put into the blow molding mold unless it keeps its original shape. However, the conventional blow molding method cannot satisfy such a condition. There is a problem that there is. That is, as shown in FIG. 8, since the temperature T _PA of the outer surface of the preform is always higher than the temperature T _PB of the inner surface, it is necessary to mold the temperature T _{PB of the} inner surface by the conventional heating method. When the preform is blown up into the mold by raising it to a temperature, the temperature T _PA of the outer surface of the preform greatly exceeds not only the temperature required for molding but also the melting point. Will be melted. Therefore, in blow molding of polyethylene terephthalate or the like, the molding temperature is set much lower than the melting point, and the insufficient amount of heat is compensated for by increasing the pressure of compressed air during blow molding. However, like blow molding of polypropylene,
When the molding temperature must be set close to the melting point, the temperature T _A of the outer surface of the preform becomes excessively high before the temperature T _{PB of the} inner surface rises to the temperature required for molding. , The preform cannot keep its original shape.

In view of the above points, the object of the present invention is to
Blow molding that compresses the temperature difference between the inner surface and the outer surface of the preform, and further raises the temperature of the inner surface of the preform higher than the temperature of the outer surface so that the preform can be blow molded in the optimum temperature condition. To realize the method.

Another object of the present invention is to realize a blow molding method capable of raising the inner surface of a preform to a predetermined temperature without excessively heating the outer surface.

[0007]

In order to solve the above problems, according to the present invention, a heating step of radiantly heating a preform molded in a bottomed cylindrical shape while rotating it about its axis, and by this heating step In a blow molding method having a molding step of blow molding a heated preform in a blow molding die, after performing the heating step, before performing the molding step, in a state where radiant heating for the preform is stopped. It is characterized by performing a cooling step of blowing a cooling gas to the outer surface of the preform while rotating the preform to cool the preform from the outer surface side.

In the present invention, the cooling step is preferably performed so that the temperature of the outer surface of the preform is lower than the temperature of the inner surface thereof.

In the present invention, it is preferable to repeat the heating step and the subsequent cooling step before the molding step.

Such a blow molding method can be performed by, for example, polyethylene terephthalate resin, polypropylene resin, polyethylene resin, polyethylene-2,6.
-It can be applied to blow molding from a preform made of a naphthalate resin, a polyamide resin, a polyarylate resin, or a polyvinyl chloride resin.

[0011]

In the blow molding method according to the present invention, the cooling gas is blown to the outer surface of the preform while rotating the preform while the radiant heating for the preform is stopped before the molding step is performed, so that the preform is formed. Since the cooling process of cooling from the outer surface side is performed, the temperature difference between the inner surface and the outer surface of the preform can be compressed in a short time, and further, the temperature of the inner surface of the preform is made higher than the temperature of the outer surface. be able to. Therefore, since the temperature of the inner surface of the preform having a high blow ratio can be higher than that of the outer surface to perform blow molding, the preform can be reasonably blow molded.

In the present invention, when the heating step and the cooling step are repeated, the preform is intermittently radiantly heated, and is cooled from the outer surface every time radiant heating is stopped. Therefore, the preform is
Even when subjected to radiant heating, the temperature difference between the inner and outer surfaces is always small and excessive heating of the outer surface is avoided. Therefore, even when the molding temperature must be set close to the melting point, the outer surface exceeds the temperature required for molding until the inner surface of the preform rises to a predetermined temperature. It does not exceed the melting point.

[0013]

Embodiments of the present invention will be described below with reference to the drawings.

(Overall Structure) FIGS. 1 and 2 show the overall structure of a blow molding apparatus to which the present invention is applied.
The blow molding apparatus 1 of this example is for performing blow molding of a PET bottle, and stretch-molds a bottomed cylindrical (test tube-shaped) preform P with one end open,
This is for molding a container B for soft drinks or the like.

As shown in FIG. 1, the apparatus 1 of the present example receives two preforms P (P1, P2) from the preform transfer station 2 at the left end of the figure, and forms a molded container B (B1). , B2) from the container take-up station 3 to the subsequent processing station (not shown). A linear transport path is formed between the transfer station 2 and the take-out station 3, and along the transport direction of this transport path, the pre-stage heating station 4, the middle-stage heating station 5, the final-stage heating station 6, and The stretch molding machine 7 is arranged in this order. The stretch molding machine 7 is provided with a blow molding die 71 for blow molding the preform P therein.

(Heating Station and Stretch Molding Machine) The preform P, which is conveyed on the conveying path while rotating about its axis, is first heated to a predetermined temperature in the pre-stage heating station 4 (first heating). Process). Next, in the middle heating station 5, it is again heated to a predetermined temperature (second heating step). After that, in the latter heating station 7, it is heated again to a predetermined temperature (third heating step). Next, it is stretch-molded in the stretch-molding machine 7 and molded into the container B (molding step).

(Conveying Mechanism) The conveying mechanism for conveying the preform P along the conveying path is a first conveying section for conveying the preform P received from the preform delivering station 2 to the entrance of the stretch molding machine 7. 8 and the preform P from the transport unit 8
Second conveying section 9 for performing molding in the container, and container B after molding
Third transport section 1 for transporting the paper to the take-out station 3
1 is comprised.

With reference to FIGS. 1 and 2, the structure of the first carrying section 8 of this embodiment will be described. The carrying section 8 includes a beam 81 arranged along a carrying line, a plurality of preform carrying tools 82 arranged on the upper surface of the beam 81, and a carrying mechanism for moving the beam 81 back and forth along the carrying direction. 83, an elevating mechanism 84 for elevating and lowering the beam 81, and a preform holding mechanism 85 arranged along the transfer line.

A plurality of transfer tools 82 arranged on the upper surface of the beam 81 are arranged at regular intervals L along the transport direction of the preform P. Each transfer tool 82 includes a rod 821 rotatably supported with respect to the beam 81, a preform carrying surface 822 formed on the upper end of the carrying tool 82, and an insertion rod 82 extending vertically from the center of the carrying surface 822.
Three. The beam transfer mechanism 83 uses the beam 81.
Has a supporting portion 831 supporting the
Are supported by rollers 832 so as to be movable forward and backward in the transport direction by a beam lifting mechanism 84.
Further, one end of the beam support portion 831 is connected to a link mechanism 833 that swings back and forth in the transport direction via a link mechanism (not shown).
The beam support portion 831 can move forward and backward in the transport direction at a constant pitch due to the swinging by the. In this example, it is possible to move at a constant feed pitch of 2L.

The beam elevating mechanism 84 comprises the beam supporting portion 831 and an elevating guide 841 which supports the beam supporting portion 831 so as to be capable of ascending and descending with respect to the apparatus mount 1A via a roller 832. . The beam support portion 831 is
The link mechanism 841 is configured to move up and down with a constant width. In this example, the beam transfer and the lifting operation are performed by a driving force from the same driving source via the link mechanism. As such a link mechanism, various structures can be used, and since it is a known technique to those skilled in the art, the details thereof will be omitted in this specification.

Here, in this example, the lower end of the rod 821 constituting the transfer tool 82 is connected to the motor 825 attached to the beam support portion 831 via the pulley and belt mechanism 824. , With this motor,
It is designed to rotate about its axis.

Next, as shown in FIGS. 2 and 3, the holding mechanism 85 of this example includes a pair of holding plates 851 and 852 arranged on the left and right in the carrying direction. These holding plates 8
51 and 852 have a bilaterally symmetrical structure.
It is supported by the gantry 1A so as to be movable left and right. As can be seen from FIG. 3, semicircular depressions 853 and 854, which have the same pitch as the outer diameter of the base end portion of the preform P, are formed on the inner edges of the holding plates 851 and 852 at a constant pitch L. There is. Therefore, in the state where these holding plates are put together, a circular preform holding portion is formed by the left and right semicircular depressions. The opening / closing operations of the left and right holding plates 851 and 852 are also configured to be performed by the same drive source 80 as the beam 81 via a link mechanism or the like.

(Preform Feeding Operation) With reference to FIGS. 4 and 5, the preform P transporting operation in the first transporting section 8 of the present embodiment thus constructed will be described. Each transfer tool 82 on the beam 81 is assumed to be at an initial position 82A on the front side in the transport direction A shown in FIG. 4 (A). In this state, the pair of left and right holding plates 851 and 852 forming the holding mechanism 85 are in a closed state, and therefore, as shown in FIG.
As shown in (B), the preform P is sandwiched (time T0 in FIG. 5). From this state, first, the elevating mechanism 84 descends to the lower second position 82B (time point T1 in FIG. 5). This lowering causes the insertion rod 823 of the transfer tool 82 to come out of the mouth of the preform P.

Next, the beam 81 is retracted backward by 2L by the beam transfer mechanism 83. As a result, the holder 82 reaches the retracted third position 82C (time T2 in FIG. 5). Then, the beam elevating mechanism 84 raises the beam 81 to the retracted position 82D. Here, this retracted position 82D is different from the initial position 82A.
This is a position two pitches behind the holder 82, and in this position, the preform P is held by the holding mechanism. Therefore, when the beam 81 rises,
The insertion rod 823 of the transfer tool 82 is inserted from the mouth of the preform P, and the preform P is held by the carrying surface 82 of the transfer tool.
2. A supported state is formed on 2 (time T in FIG. 5).
3). After this, as shown in FIG. 4C, the holding mechanism 8
5, the pair of holding plates 851 and 852 are opened (time T4 in FIG. 5). As a result, the preform P is supported only by the transfer tool 82. After this, the beam transfer mechanism 83 advances the transfer tool 82 again to its initial position 82A (time T5 in FIG. 5). Here, since the rod 821 of the transfer tool 82 is constantly rotating, the preform P supported by the rod 821 is also always rotated and conveyed. After that, the holding plates 851 and 852 of the holding mechanism 85 are closed again to form a state in which the preform P is held (time T6 in FIG. 5).

Thus, in this example, the beam 81
The preforms P are conveyed at a constant feed pitch 2L by the transfer tools 82 that move together with the transfer tools 82.
Then, the transfer tool 82 and the motor 8 for rotating the transfer tool 82.
The preform P is conveyed in a state of being rotated around its axis by a rotating means utilizing 25. However, the preform P is not rotated when it is sandwiched by the pair of holding plates 851 and 852.

After the carrying operation is performed once, as shown in FIG. 5, in the stretch molding machine 7, the preform carried therein is molded (time T7 to T8). The stretching operation of the stretch-molding machine 7 of this example is the same as that of a generally used machine, and therefore the description of its structure and operation will be omitted.

After that, the same cycle is repeated to carry out the conveying and forming operations of the preform.

Next, in the present example, the preform P is received from the first transporting section 8 having the above-mentioned configuration, and the stretch molding machine 7 is provided.
The second transfer section 9 that is carried into the container is also basically the first transfer section 8
Is configured similarly to. However, as can be seen from FIG. 1, the second transport section 9 is provided with a pair of transfer tools 91, 92, and these retracted positions 91A,
The distance L at 92A is different from the distance L2 inside the molding machine. In order to make the feed pitch different in this way, the feed pitch may be set differently by using a cam and a link mechanism. Or,
The feed pitch may be made different by forcibly bringing the plurality of transfer tools slidable via compression springs into close contact with each other or separating them. Various types of such mechanisms can be adopted. This second transport section 9
Then, the configuration is the same as that of each of the transfer tools in the first transfer unit 8 except that a pair of transfer tools are provided as described above, the feed pitches thereof are different, and the preform rotation mechanism is not provided.

On the other hand, the third transfer section 11 is also basically the first
Is the same as the transport unit 8 of FIG.
And transfer them at the same feed pitch, and take out two containers B1 and B2 after molding from the molding machine 7,
It is carried out toward a processing station (not shown) on the rear side.
The configuration of this transport unit is also the same as that of the first transport unit 8 except that the feed pitch is different and that a rotation mechanism for the molded product is not provided.

(Temperature Control of Preform) Next, the temperature control mechanism and temperature control operation of the preform P in the apparatus of this embodiment will be described.

FIG. 6 schematically shows a plane structure of a conveying path from the first heating station 4 to the stretch molding machine 7. As shown in this figure, near-infrared heaters 48, 58, 68 are provided inside the first-stage heating station 4, the middle-stage heating station 5, and the final-stage heating station 6 on one side of the conveyance path along the conveyance direction. It is arranged. Therefore, the outer surface PA of the preform P is passed through the first heating station 4, the middle heating station 5, and the final heating station 6 while the infrared heater 4
Radiation heating from 8, 58, and 68 is received, and the whole is heated uniformly.

Here, between the first heating station 4 and the middle heating station 5, the first heating station 4 is
A first cooling mechanism 40 for cooling the radiantly heated preform P from the outer surface PA is attached.
In this first cooling mechanism 40, an air ejection port 41 arranged on the side of the conveyance path, a blower pipe 42 connected to this air ejection port 41, and an air ejection port 41 via this blower pipe 42. And a blower fan 10 for sending cooling air to. The blown air from the blower fan 10 is blown from the air blowout port 41 toward the outer surface PA of the preform P conveyed while rotating there between the first stage heating station 4 and the middle stage heating station 5, The entire circumference is cooled (first cooling step). In this cooling process, the radiant heating for the preform P is stopped.

Further, a second cooling mechanism 50 for cooling the preform P radiatively heated in the intermediate heating station 5 from the outer surface PA is attached between the intermediate heating station 5 and the final heating station 6. Has been. The second cooling mechanism 50 includes an air ejection port 51 arranged on the side of the conveyance path and a blower pipe 52 connected to the air ejection port 51, and the first cooling mechanism 40. The air blown from the blower fan 10 common to the air blower is blown from the air blowout port 51 between the intermediate heating station 5 and the final heating station 6 toward the outer surface PA of the preform P conveyed while rotating there. It is turned on, and the entire circumference thereof is cooled (second cooling step). Even in this cooling step, the radiant heating for the preform P is stopped.

Further, between the final heating station 6 and the stretch molding machine 7, there is provided a third cooling mechanism 60 for cooling the preform P radiatively heated in the final heating station 6 from the outer surface PA. Installed. The third cooling mechanism 60 also includes an air ejection port 61 disposed on the side of the transport path and a blower pipe 62 connected to the air ejection port 61, and the first and second cooling mechanisms are provided. The blown air from the blower fan 10 that is common to the cooling mechanisms 40 and 50 is
Between the final stage heating station 6 and the stretch molding machine 7, air is blown from the air ejection port 61 toward the outer surface PA of the preform P conveyed while rotating there, and the entire periphery thereof is cooled (No. 3 cooling step). Even in this cooling step, the radiant heating for the preform P is stopped.

(Operation and Effect of Blow Molding Apparatus of the Present Example) In the blow molding apparatus 1 thus constructed,
From preform delivery station 2 to preform P
, The preform P remains at room temperature. However, while the preform P is conveyed while being rotated on the conveying path and is carried into the stretch molding machine 7, the preform P reaches a predetermined temperature in the initial heating station 4, the intermediate heating station 5, and the final heating station 6. Be heated.

Here, at the outlet of each heating station,
The 1st thru | or 3rd cooling mechanism 40,50,60 is comprised, and air is blown toward the outer surface PA of the preform P from each air ejection port 41,51,61. Therefore, as shown in the period t11 in FIG. 7, for example, in the final heating station 6, the preform P is
Is radiatively heated from the outer surface PA by the near infrared heater 68, the temperature T of the outer surface PA of the preform P is
_{In PA} , the temperature T _PA of the outer surface _PA is higher than the temperature T _PB of the inner surface PB. However, as shown in period t12 in FIG. 7, when the final stage heating station 6 is exited, the radiant heating for the preform P is stopped, and at the same time, air is received from the air ejection port 61 of the third cooling mechanism 60, The reform P is cooled from its outer surface PA. Therefore, when the period t12 in FIG. 7 ends, the inner surface P
The temperature T _PB of B is higher than the temperature T _PA of the outer surface PA. Therefore, in the period t13, the preform P is
Temperature T _PB in the inner surface PB is loaded into the stretch-molding machine 7 at a higher than the temperature T _PA of the outer surface PA state, it is blow molding in a state of such a temperature distribution. That is, the temperature of the inner surface PB of the preform P having a high blow ratio is set to the outer surface P
Since it can be blow-molded at a temperature higher than A, the preform P can be blow-molded as a whole without difficulty. Moreover, since cooling is performed in a state where heating of the preform P is stopped, it is possible to cool to a predetermined temperature in a short time.

Further, in this example, the first to third cooling mechanisms 4 are provided to the outlets of the first heating station 4, the middle heating station 5, and the final heating station 6.
Since 0, 50 and 60 are respectively configured, the heating process and the cooling process are repeated. Therefore, the preform P is radiatively heated intermittently, and
Since the outer surface PA is cooled every time the radiant heating is stopped, even if the preform P receives the radiant heating, the temperature difference between the inner and outer surfaces of the preform P is always small, and excessive heating of the outer surface PA is avoided. It Therefore, of course, as in the case of molding polyethylene terephthalate or the like, the molding temperature can be set much lower than the melting point, and as in the case of molding polypropylene or the like, the molding temperature must be set close to the melting point. Even if there is not, the inner surface PB of the preform P
The outer surface PA does not exceed the temperature required for molding and further significantly exceeds the melting point before the temperature rises to a predetermined temperature. Therefore, even if the inner surface PB of the preform P is raised to the required temperature, the outer surface PA will not be melted and the trouble will not occur.

(Other Embodiments) In this embodiment, the transport path of the preform P is linear, and the heating station and the cooling station are arranged in the middle of the transportation path. The preform P may deviate at an intermediate position and the cooling process may be performed at another position.

In addition, the blow molding method of this example is not limited to polyethylene terephthalate resin and polypropylene resin, but polyethylene resin, polyethylene-2, 6-
It can be applied to blow molding from a preform made of a naphthalate resin, a polyamide resin, a polyarylate resin, or a polyvinyl chloride resin.

[0040]

As described above, in the present invention, since the cooling step of cooling the preform from the outer surface side is performed with the radiant heating for the preform stopped,
The temperature difference between the inner surface and the outer surface of the preform can be compressed in a short time, and further, the temperature of the inner surface of the preform can be made higher than the temperature of the outer surface _. Therefore, according to the present invention, since the temperature of the inner surface of the preform having a high blow ratio can be higher than that of the outer surface, the blow molding can be performed, so that the preform can be blow molded as a whole without any difficulty.

When the heating step and the cooling step are repeated, the preform is intermittently radiantly heated, and is cooled from the outer surface every time the radiant heating is stopped. The temperature difference between the inner and outer surfaces is always small and excessive heating of the outer surface is avoided. Therefore,
Before the inner surface of the preform rises to a predetermined temperature, the outer surface does not exceed the temperature required for molding, and further does not exceed the melting point. Therefore, even if the inner surface of the preform is heated to the required temperature, no trouble such as melting of the outer surface occurs.

[Brief description of the drawings]

FIG. 1 is a schematic side view showing a configuration of a blow molding apparatus that is an embodiment of the present invention.

2 is a schematic cross-sectional view of the device of FIG.

FIG. 3 is a partial plan view showing a pair of holding plates which constitute a holding mechanism for a preform in the apparatus shown in FIG.

4A and 4B are views for explaining a transfer operation in the apparatus of FIG. 1, and FIG. 4A is an explanatory view showing movement of each transfer tool;
(B) And (C) is explanatory drawing which shows operation | movement of a preform holding mechanism.

5 is a time chart showing the operation of the apparatus of FIG.

FIG. 6 is a plan view schematically showing the configuration of the apparatus of FIG. 1 from the first-stage heating station to the stretch molding machine.

7 is a graph conceptually showing a temperature profile of the preform during the period from the latter heating station of the apparatus of FIG. 1 to the time when it is carried into the stretch molding machine.

FIG. 8 is a graph conceptually showing a temperature profile of a preform from a heating station of a conventional apparatus to being carried into a stretch molding machine.

FIG. 9 is an explanatory diagram for comparing and explaining a difference in blow magnification between an inner surface and an outer surface when a bottle is blow-molded from a preform.

[Explanation of symbols]

 1 ... Blow molding apparatus 3 ... Ejection station 4 ... Pre-heating station 5 ... Middle heating station 6 ... Post-heating station 7 ... Stretch molding machine 8, 9, 11 ... Conveyance Mechanism 10 ... Blower fan 40 ... First cooling mechanism 41 ... Air ejection port 50 ... Second cooling mechanism 51 ... Air ejection port 60 ... Third cooling mechanism 61. ..Air ejection port 68 ... Near infrared heater B (B1, B2) ... Container (bottle) P (P1,2) ... Preform PA ... External surface of preform PB ... Preform Inner surface of

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Claims (4)

[Claims] 1. A heating step of radiatively heating a preform molded in a bottomed tubular shape while rotating it about its axis,
In a blow molding method having a molding step of blow molding a preform heated by this heating step in a blow molding die, after performing the heating step, before performing the molding step, radiation to the preform With heating stopped,
A blow molding method, which comprises performing a cooling step of blowing a cooling gas to the outer surface of the preform while rotating the preform around its axis, and cooling the preform from the outer surface side. 2. The blow molding method according to claim 1, wherein the cooling step is performed so that the temperature of the outer surface of the preform becomes lower than the temperature of the inner surface thereof. 3. The blow molding method according to claim 1, wherein the heating step and the subsequent cooling step are repeated before the molding step. 4. The preform according to any one of claims 1 to 3, wherein the preform is a polyethylene terephthalate resin, a polypropylene resin, a polyethylene resin,
A blow molding method comprising a resin selected from the group consisting of polyethylene-2,6-naphthalate resin, polyamide resin, polyarylate resin, and polyvinyl chloride resin.