JPH06344427A - Method and device for molding - Google Patents

Abstract

PURPOSE:To maintain a specific shape of a preform used for biaxially orientational blow molding and secure a specific temperature distribution by heating the bottom and the external and internal wall surfaces of the perform which has not reached the proper temperature for regulating the temperature of the preform. CONSTITUTION:A preform P is cooled in a time for injection molding for suppressing heat shrinkage deformation and maintained at the temperature not higher than a proper temperature for orientation in a time for biaxially orientational blow molding. A temperature regulation core 14 is inserted into the inside of the preform P arranged in a temperature regulation pot 12. At the time, the position of the temperature regulation core 14 is regulated to the position wherein a first core part 14A approaches the bottom internal wall surface of the preform P. Further the outside dimension of the temperature regulation core 14 is regulated smaller than the dimension of the inside shape of the preform P at the temperature not higher than the proper temperature for orientation. Therefore, a second core part 14B approaches the internal wall surface of the drum part of the preform P.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION This invention relates to a method and apparatus for reheating preforms.

[0002]

2. Description of the Related Art Generally, a thin-walled container made of synthetic resin, which is generally called a biaxially stretch blow-molded container, has a preform obtained by, for example, injection molding, which is positioned in a cavity of a blow mold so that the preform is axially moved. It is obtained by stretching and expanding in the direction perpendicular to the axial direction by the pressure of the gas blown inside.

By the way, some resin materials which are subjected to such a molding process cause large heat shrinkage. As an example, there is a styrene resin having impact resistance called HIPS (high impact styrene) among styrene resins, a high density or low density PE (polyethylene) resin. Usually, a preform molded from a resin material is cooled in the injection cavity mold and set to a temperature at which it can be released. But,
These resins require a large amount of heat in order to bring the preform to an appropriate temperature for stretch blow. For this reason, if the preform is quickly released from the injection mold and the preform is kept at a high temperature, heat shrinkage deformation easily occurs in the molded preform. Therefore, in the case of heat shrinkage deformation, not only the shape becomes smaller, but also a shape change such as bending due to uneven shrinkage rate in the longitudinal direction and the circumferential direction of the preform is included. Further, due to this shrinkage, temperature control becomes non-uniform in the temperature control process section, which is the next process, and causes uneven thickness of the bottle.

The inventor has observed this phenomenon and found that the filling state of the resin is circumferential or longitudinal depending on the type of components contained in the resin and the temperature distribution of the resin when the preform is molded. It was confirmed that heat shrinkage deformation occurs due to axial deviation and the like.

Therefore, in the biaxial stretch blow molding process, it becomes impossible to secure the stretch amount based on the predetermined shape dimension set at the stage of the preform, and the curved preform promotes the non-uniform temperature distribution. This makes it difficult to optimize the thickness distribution of the container. Further, there is a risk that the peripheral wall of the curved preform may be pierced by the stretch rod inserted into the preform.

Therefore, the preform at the time of injection molding is
Sufficient cooling is required to suppress heat shrinkage deformation.

[0007]

However, when the resin material as described above is used, if the heat shrinkage is suppressed by sufficient cooling, the temperature of the preform often becomes lower than the suitable drawing temperature. For example, in the case of the above-mentioned high-density polyethylene resin, due to the relatively high crystallization rate, it is possible to release the mold even if the cooling time is short, but the released preform is not at the suitable stretching temperature. Has been observed. Further, in the case of low density polyethylene resin, this resin material has a relatively low bending or buckling strength as compared with high density polyethylene, and is a so-called weak material, so the temperature at the time of mold release is high. And the injection mold, particularly the injection core mold, may remain in close contact with the mold, and the shape may be inverted as the injection core mold moves upward. Therefore, this resin material had to be cooled until it was sufficiently solidified. Further, in the case of HIPS, since it has a rubber component, if the temperature at the time of releasing from the injection mold is high, the shrinkage becomes large. In this way, after injection molding, the preform that is not at the optimum stretching temperature required for biaxial stretching blow is
Temperature adjustment such as reheating is required before stretch blow molding.

Therefore, in the temperature adjusting step for setting the preform after injection molding to a suitable stretching temperature, the temperature of the preform is adjusted by using the structure shown in FIG. 5 or 6, for example.

In FIG. 5, the preform P is arranged in the temperature control pot A or in a state of facing the heating member (not shown), and the outer layer of the preform P is from the heating surface of the temperature control pot A. It is heated by radiant heat. On the other hand, the inner layer of the preform is temperature controlled using the following structure. For example, in the case of using the temperature control pot A, in order to increase the retained heat immediately under the neck portion that comes into contact with the cavity surface earliest during stretch blow molding, a structure in which a heating piece B facing this position is arranged, or As shown in FIG. 6, there is a structure in which a heater rod C that can heat the entire preform P in the longitudinal direction is arranged.

Each of the structures for adjusting the temperature inside the preform P is provided with a heat source close to the inner wall surface of the preform P. And this heat source and temperature control pot A
The preform P heated by the above heat-shrinks and deforms in the same manner as after the above-mentioned injection molding. Therefore, the preform P may have a different proximity distance from the heat source in the circumferential direction. In this case, the temperature distribution often does not become uniform in the circumferential direction of the preform P. For this reason,
During stretch blow molding, the stretch ratio in the circumferential direction changes,
A uniform wall thickness distribution cannot be obtained. Further, the heat source may be contracted by heat and deformed to come into contact with the heat source. In this case, the temperature of the part in contact with the heat source becomes high, and the part is melted and damaged. Such a problem occurs in the temperature control process often used in the hot parison system or in the heating process before blow molding used in the cold parison system.

Therefore, an object of the present invention is to solve the problems in the above-mentioned conventional molding method, particularly, the problem when reheating is performed after injection molding to set a preform that is not at a suitable stretching temperature to a suitable stretching temperature. In view of this, it is an object of the present invention to provide a molding method and a molding apparatus capable of maintaining a predetermined shape as a preform used for biaxial stretch blow molding and ensuring a predetermined temperature distribution for stretch blow molding.

[0012]

In order to achieve this object, the invention according to claim 1 is a method for molding a hollow container by biaxially stretch-blow molding an injection-molded preform. Before the axial stretch blow molding, there is a step of heating the outer wall surface and the inner wall surface of the preform bottom and body that have not reached the appropriate stretching temperature to adjust the temperature to the appropriate stretching temperature. It is also possible to set the preform at an appropriate temperature for stretching while controlling the thermal deformation of the preform that has been heat-contracted during the temperature control by using a temperature adjusting means having a small external dimension that can be inserted in a non-contact state. It has a feature.

In a molding apparatus for molding a hollow container by biaxially stretch-blow molding an injection-molded preform, an outer peripheral surface of the preform is heated until a temperature suitable for stretching is reached. And a temperature control pot that can be placed inside the preform and is smaller than the inner shape dimension of the preform that has not reached the appropriate stretching temperature,
The outer shape is formed by dimensions that can be inserted in a non-contact state,
And a temperature adjusting means that is in close contact with the inner wall surfaces of the body and bottom of the preform that are heat-shrinkable in the temperature control pot and that regulates shrinkage deformation.

According to a third aspect of the present invention, in the second aspect, the temperature adjusting member has a structure for setting a temperature distribution at least between the bottom portion and the body portion in the longitudinal direction of the preform. It is characterized by that.

[0015]

In the molding method according to the present invention, the preform which is not at the proper temperature for stretching after injection molding is reheated before the biaxial stretch blow molding. At this time, the preform undergoes thermal contraction, but the temperature degree adjusting means inserted in a non-contact state causes thermal deformation due to contact between the inner wall surfaces of the body and bottom of the preform during thermal contraction. The temperature is regulated and set to an appropriate temperature for stretching while maintaining a predetermined shape as a preform to be subjected to biaxial stretch blow molding. Further, since the temperature adjusting means does not contact the inner wall surface of the preform during insertion,
Does not scratch the inner wall surface of the preform.

In the molding apparatus according to the present invention, when reheating a preform that is not at a suitable drawing temperature to set it at a suitable drawing temperature, the inner wall surfaces of the bottom and the body of the preform, which shrink due to the heating, are set inside the preform. It can be formed in an outer size smaller than the shape and can be brought into close contact with the temperature adjusting means inserted in a non-contact state. For this reason, the preform is regulated to have its inner wall surface deformed and maintained in a predetermined shape, and at this state, an appropriate stretching temperature is set.

Further, in the molding apparatus according to the present invention, when the preform is reheated, it is possible to set the temperature distribution in the vertical axis direction, particularly the temperature distribution between the bottom portion and the body portion. This prevents the temperature of the bottom of the preform, which is in a relatively high temperature after injection molding, from rising, and stabilizes the amount of stretching from the bottom including the gate marks that affect the wall thickness distribution of the container. Can be made.

[0018]

The present invention will be described in detail below with reference to the illustrated embodiments.

FIG. 1 is a sectional view showing a temperature controller 10 used in the molding method according to the present invention.

That is, the temperature control device 10 is for setting the preform to an appropriate stretching temperature before the biaxial stretch blow molding which is performed after the injection molding, and includes the temperature control pot 12 and the temperature control means 14. ing. The temperature control pot 12 includes a plurality of heating units 1 zoned in the longitudinal direction of the preform P.
6, a predetermined temperature is maintained by a heat source (not shown). The predetermined temperature in this case corresponds to the temperature at which the bottom and the body of the preform P are set to have suitable stretching temperatures.

On the other hand, the temperature adjusting means 14 is arranged inside the preform P. That is, the temperature adjusting means 14
Is composed of a core member (hereinafter referred to as a temperature adjustment core 14). The temperature adjusting core 14 sets the temperature distribution of the inner wall surface of the preform P to be reheated in the temperature adjusting pot and is heated to adjust the temperature of the preform P.
Are provided to define the shape and dimensions when heat shrinks. For this reason, the temperature adjustment core 14 has the preform P.
The outer size of the position facing the bottom and the body is set to be smaller than the inner shape of the preform P that is at or below the appropriate stretching temperature after injection molding. Therefore, the temperature adjustment core 14 can be inserted into the preform in a non-contact state. Further, on the surface of the temperature adjustment core 14, a release layer using fluororesin such as Teflon (trade name) or Caniflon is provided. As a result, the preform P heated by the temperature adjusting pot 12 has its temperature distribution adjusted in the vertical axis direction, and adheres to the outer peripheral surface of the temperature adjustment core 14 when heat shrinks in the vertical axis direction and the circumferential direction. To do. For this reason, the preform P is heated in a state defined by the shape and dimensions required for the biaxial stretch blow molding until it reaches the proper stretching temperature. Further, when the inner wall surface of the preform P comes into close contact with the outer peripheral surface of the temperature adjustment core 14, the preform P
The inner wall surface of the may melt. As a result, when the temperature adjusting core 14 is detached, the surface may be dragged to change the planarity, but such a phenomenon is prevented by the release layer. Further, when the inner wall surface of the preform P is rubbed, the temperature adjusting core 14 is inserted, but in the present embodiment, the flatness of the inner wall surface of the preform is impaired because the inner wall surface of the preform is not in contact. Never.

On the other hand, the temperature adjusting core 14 has a structure for setting the temperature distribution between the bottom and the body in the longitudinal direction of the preform P.

That is, the temperature adjusting core 14 is provided with a first core portion 14A and a second core portion 14B from the tip end side along the vertical axis direction. The first core portion 14A is a member that faces the inner wall surface of the bottom portion of the preform P that has not reached the appropriate drawing temperature and sets the temperature of this portion, and the second core portion 14B is inside the body portion of the preform P. It is a member that faces the wall surface and sets the temperature of this portion. First core part 1
4A and the second core portion 14B are connected and integrated by a heat insulating material 18 interposed therebetween.

The heat insulating material 18 is provided to prevent heat conduction from the second core 14B. That is, the bottom portion of the preform P often has a higher temperature than other portions because it corresponds to the resin introduction position during injection molding. Therefore, if the temperature of this portion is further increased by reheating, the stretching ratio in this portion including the gate mark may change. Therefore, the wall thickness distribution in the container to be set at the time of the biaxial stretch blow molding may be different. Therefore, by maintaining this part in a state where it is not affected by the temperature from other parts, that is, in a state where the temperature does not rise, the amount of resin stretched from the bottom including the gate mark to the body is regulated. Will be required. Therefore, the second core portion 1 facing the first core portion 14A
A cavity is formed inside the tip of 4B, and a heat insulating material 18 made of, for example, ceramics is inserted into the cavity. The first core portion 14A is attached to the lower end side of the heat insulating material 18. Therefore, the heat transfer from the second core portion 14B to the first core portion 14A is blocked by the heat insulating material 18 located inside the cavity, so that the contact between the outer surface of the first core 14A and the outer peripheral surface of the first core 14A can be prevented. The reform P is maintained in a state where the temperature of the bottom portion does not rise.
The core portion 14A may be made of a heat insulating material or the like.

It should be noted that, instead of inserting the heat insulating material 18 into the cavity portion of the second core portion 14B shown in FIG. 1, as shown in FIG. A laminated structure in which the outer peripheral surface is exposed by being sandwiched between the portion 14B and the portion 14B may be used. Moreover, you may comprise the 1st whole core part with a heat insulating material. Then, the distance (L) from the tip of the temperature adjusting core 14 to the upper end position of the heat insulating material 18 or the thickness of the heat insulating material 18 is set in consideration of the stretching characteristics at the bottom of the preform P and the amount of heat retained in this portion. Must be set so that That is, if this distance is too long or the heat insulating material 18 is too thick, the amount of stretching at the bottom of the preform P becomes too small, and the thickness distribution cannot be optimized. In this embodiment, the distance (L) is 5 to 20 mm.
Is set to. However, this value can be changed depending on the shape, length or wall thickness of the preform P.

Next, a molding method will be described based on the structure of the molding apparatus.

The preform P injection-molded from the resin material is placed in the temperature control pot 12. At this time, the preform P is cooled at the time of injection molding and is maintained at a temperature equal to or lower than the suitable stretching temperature at the time of biaxial stretch blow molding for the purpose of suppressing heat shrinkage deformation. Then, the temperature adjustment core 14 is inserted inside the preform P arranged in the temperature adjustment pot 12. The position of the temperature adjusting core 14 at this time is such that the first core portion 14A is close to the inner wall surface of the bottom of the preform P, and the external dimensions of the temperature adjusting core 14 are below the appropriate drawing temperature. The second core portion 14B is also close to the inner wall surface of the body portion of the preform P because it is smaller than the inner shape dimension of. Therefore, due to the difference in shape and size, the temperature adjustment core 14 is inserted without contacting the inner wall surface of the preform P. This prevents the inner wall surface of the preform P from being rubbed.

On the other hand, when heated by the temperature control pot 12, the preform P undergoes thermal contraction deformation. Then, the preform P is thermally contracted and deformed so that the preform P becomes
It is in close contact with the outer peripheral surface and is restricted from contracting and deforming further.
Further, in the temperature adjustment pot 12, the preform P that is in close contact with the outer peripheral surface of the temperature adjustment core 14 is continuously heated until the temperature reaches the optimum drawing temperature. At this time, the inner wall surface of the preform P that is in close contact with the outer peripheral surface of the temperature adjustment core 14 may be melted by being heated. Therefore, when the temperature adjusting core 14 is detached, the temperature adjusting core 14 may be dragged in an adhesive state, but in this case, the surface friction resistance is minimized by the release layer included in the temperature adjusting core 14, Drag will be suppressed. Therefore, it is possible to prevent a situation where the surface of the preform becomes rough due to being dragged.

Further, in the longitudinal direction of the preform P, a temperature distribution is set between the bottom and the body. That is, in the temperature control pot 12, the temperature distribution zoned in the vertical axis direction of the preform P is set, and the heating temperature is set so that the body of the preform has a higher temperature than the bottom. Therefore, it is preferable to set this temperature distribution also in the temperature adjustment core 14 to which the preform P is in close contact. Therefore, the first and second core portions 14A, 1
The heat insulating material 18 located between 4B does not transmit the retained heat in the second core portion 14 to the first core portion 14A. Therefore, the bottom portion of the preform P is set to a proper drawing proper temperature so as not to cause an abnormal temperature rise, so that an extremely thin wall at the time of blowing in the biaxial stretching is prevented, and an accident such as breakage due to the stretching rod occurs. Is prevented. Regarding this temperature distribution, for example, in the case of the polystyrene resin, when the suitable stretching temperature is set to 110 to 150 ° C., in the present embodiment, the body temperature of the temperature control core reaches 230 ° C. On the other hand, a distribution was obtained in which the bottom had a substantially constant temperature of 130 ° C.

Usually, when the preform P is heated for temperature control, the outer layer of the preform P is heated by radiant heat from the temperature control pot, and the inner layer is heated by a single heating member. However, it is difficult to set the temperature distribution between the bottom and the body with a single heating member. On the other hand, according to the present embodiment, the temperature distributions at both the above-mentioned parts can be easily set, so that an abnormal temperature rise at the bottom can be prevented. Therefore, it becomes possible to prevent the thickness distribution of the container, which tends to occur when the temperature of the bottom portion rises, from becoming non-uniform. In other words, when the temperature of the bottom part rises, the amount of heat retained in this part increases, and the amount of resin stretched toward the body part becomes uneven, and the wall thickness of the container tends to become uneven. By maintaining the temperature at an appropriate temperature, such a problem can be solved.

The structure for setting the temperature distribution between the bottom portion and the body portion in the vertical axis direction of the temperature adjusting core 14 is not limited to the structure of blocking the heat conduction from the second core portion 14B facing the body portion.

FIG. 3 shows a modification of the structure for setting the temperature distribution in the vertical axis direction of the temperature adjusting core 14.
In the structure shown in FIG. 3, the temperature adjustment core 14 shown in FIG.
As a structure, a temperature control unit for setting a temperature lower than that of the body of the preform P is formed in the first core portion 14C that faces the bottom of the preform P, and faces the body of the preform P. The second core portion 14D is characterized by comprising a heating portion and a temperature balancing portion. That is, inside the temperature adjusting core 14, the refrigerant passage 20 formed along the vertical axis direction is provided at the center in the radial direction.
The refrigerant passage 20 communicates with a cavity portion formed inside the first core portion 14C. A coolant such as water or oil circulates in the coolant passage 20. Therefore,
The first core portion 14C is positively cooled by the refrigerant.

Further, in the second core portion 14D, a plurality of rod-shaped heating members 22 are arranged along the circumferential direction around the refrigerant passage 20, and further, on the outer periphery of the rod-shaped heating members 22. In the vicinity of the surface of the second core portion 14D, a plurality of heat pipes 24 forming a temperature balancing portion are arranged in the circumferential direction. The heat pipes 24 are arranged mainly in places where the rod-shaped heating members 22 are not located, and
The distribution of the surface temperature of D is made uniform. Also in this case, as in the case of the embodiment shown in FIG. 1, the external dimensions at the position of the temperature adjusting core 14 are such that the external dimensions facing the bottom portion and the body portion of the preform P are suitable for stretching after injection molding. It is set smaller than the inner diameter of the preform P shown below.

In this structure, the temperature adjusting core 14 is inserted into the preform P which is heated to adjust the temperature and has a temperature not higher than the suitable drawing temperature. The temperature adjustment core 14 inserted into the preform P has an outer dimension smaller than the inner diameter dimension of the preform P, so that the temperature adjustment core 14 is easily inserted and the inner wall surface of the preform P is There is no such thing as rubbing.

On the other hand, in the temperature adjusting core 14, the first core portion 14C is cooled by the refrigerant and the second core portion 14D is heated by the rod-shaped heating member 22, so that the bottom portion of the preform P in the longitudinal direction and Set the temperature distribution between the torso. Therefore, the preform P, which is heated by the radiant heat from the temperature control pot 12, is heat-shrinkable and deformed so that the bottom portion and the body portion of the temperature control core 14 are different from the first core portion 14C and the second core portion 14D. They are brought into close contact with each other, and subsequent heat shrinkage deformation is restricted. Therefore, the preform P is continuously heated until it reaches the appropriate temperature for stretching while maintaining the predetermined shape as the preform used for the biaxial stretching blow molding.

According to such a structure, the second core portion 1
Since the heat pipe 24 is arranged inside the 4D so that it can be inserted and removed, the temperature of the preform P can be controlled in the circumferential direction. For this reason, during biaxial stretch blow molding, the amount of stretching in the circumferential direction is optimized so that the thickness distribution in the circumferential direction can be made uniform. Further, in the second core portion 14D, by positively heating, it is possible to shorten the time until the entire region in the vertical direction including the body portion of the preform P reaches the appropriate stretching temperature.

The molding method and molding apparatus according to the present invention may be applied to either the hot parison method or the cold parison method.

[0038]

As described above, according to the method of the present invention, when a preform that has not reached the appropriate drawing temperature after injection molding is heated to adjust the drawing temperature before biaxial stretching blow molding, Even if the heated preform undergoes heat shrinkage, it is possible to regulate shrinkage deformation by using a means that is inserted in a non-contact state and contacts the inner wall surfaces of the body and bottom of the preform. Therefore, the preform that has not reached the appropriate drawing temperature is set to the appropriate drawing temperature while maintaining the predetermined shape as the preform used for the biaxial stretching blow molding. Moreover, when the regulation means is inserted into the preform, it is not in contact with the preform so that the inner wall of the preform is not damaged.

Further, according to the molding apparatus of the present invention, when heating the preform which has not reached the appropriate drawing temperature for adjusting the temperature to the appropriate drawing temperature, it is inserted in advance in a state of not contacting the inner wall surface of the preform. The shape of the inner wall surface of the preform, which is formed into a shape and is heat-shrinked by heating, is provided in close contact with the inner wall surface of the bottom portion of the preform and the inner wall surface of the body portion. Moreover, the preform can be set to a suitable stretching temperature while maintaining the predetermined shape.

Further, since the temperature adjusting means for controlling the heat shrinkage deformation of the preform can set the temperature distribution between the bottom portion and the body portion in the longitudinal direction of the preform, it is possible to set the temperature suitable for stretching. It is possible to shorten the cycle time and set the temperature at which the required wall thickness distribution can be obtained in each part.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a configuration of a molding apparatus used in a molding method of the present invention.

FIG. 2 is a cross-sectional view showing a part of a modification of the molding apparatus shown in FIG.

FIG. 3 is a cross-sectional view showing a modified example of the main part of the molding apparatus shown in FIG.

FIG. 4 is a sectional view taken along the line CC in FIG.

FIG. 5 is a schematic view showing an example of a temperature control structure.

FIG. 6 is a schematic view showing another example of the temperature control structure.

[Explanation of symbols]

 10 Reheating Temperature Control Device 12 Temperature Control Pot 14 Temperature Control Core 14A, 14C First Core Portion 14B, 14D Second Core Portion 18 Insulation Material 20 Refrigerant Passage 22 Heating Member 24 Heat Pipe

Claims (3)

[Claims] 1. A method for forming a hollow container by biaxially stretch-blowing an injection-molded preform, comprising a bottom portion of a preform that has been performed before biaxially stretch-blowing and has not reached an appropriate stretching temperature. And a step of heating the outer wall surface and the inner wall surface of the body part to adjust the temperature to an appropriate temperature for stretching, and a temperature adjusting means having an outer size smaller than the inner diameter of the preform and insertable in a non-contact state. A molding method, wherein the preform is set to an appropriate temperature for stretching while controlling the thermal deformation of the preform that is heat-shrinked during the temperature control. 2. A molding apparatus for molding a hollow container by biaxially stretch-blow molding an injection-molded preform, comprising: a temperature control pot for heating the outer peripheral surface of the preform until a temperature suitable for stretching is reached; It can be arranged inside the preform and is smaller than the inner shape dimension of the preform that has not reached the appropriate stretching temperature, and the outer shape is formed by a dimension that can be inserted in a non-contact state, and inside the temperature control pot. A molding apparatus, comprising: a temperature adjusting unit that is in close contact with inner wall surfaces of a body portion and a bottom portion of a preform that undergoes heat shrinkage and regulates shrinkage deformation. 3. The molding according to claim 2, wherein the temperature adjusting member has a structure for setting a temperature distribution between at least a bottom portion and a body portion in a longitudinal direction of the preform. apparatus.