JPH06226830A - Releasing method for preform - Google Patents

Abstract

PURPOSE:To provide a method for releasing a preform from a mold without releasing malfunction even if a releasing temperature is high. CONSTITUTION:An injection core 40 is first driven upward. At an initial stage of this releasing step, the air is introduced between a core pin 44 and an inner wall of a preform 10. Radial deformation of the preform 10 cap be restricted by a cavity surface 32 of an injection cavity mold 30 disposed around the preform 10. The preform 10 is not deformed by a reason such as restriction of opening lip molds 20 by engaging an annular tapered part 22 of the molds 20 with a tapered hole 38 of the mold 30, an end face 46 of the pin 44 is not in contact with a bottom inner wall 16 of the preform 10 to be easily released.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a preform releasing method capable of preventing defective releasing.

[0002]

2. Description of the Related Art In order to blow mold a hollow container such as a bottle, it is necessary to injection-mold a preform in advance.
FIG. 4 shows a mold clamping state of a mold for injection molding the preform 10. The preform 10 includes an open lip portion 12 and a bottomed tubular body portion 1 on the lower end side thereof.
4 and. In order to injection-mold this preform 10, a lip mold 20, an injection cavity mold 30, and an injection core mold 40 shown in the figure are used. Lip type 2
0 is a pair of split molds 20 that can be opened in the left-right direction in FIG.
a and 20b, and has a cavity surface that defines the outer wall of the lip portion of the preform 10. The injection cavity mold 30 has a cavity surface 32 that defines the outer wall of the body portion 14 of the preform 10, and a gate 34 that communicates with the cavity surface 32 at the lower end thereof. The injection cavity mold 30 has a refrigerant passage 36 formed therein,
The injection-molded preform 10 can be cooled to a predetermined temperature. The injection core mold 40 includes a base end portion 42 and a core pin 44, and the core pin 44 defines the inner wall of the preform 10. This injection core type is also provided with a refrigerant passage (not shown).

After the molds 20, 30 and 40 are clamped as shown in FIG. 4, resin is filled from the gate 34 to perform injection molding of the preform 10. Also,
Since the coolant is circulated and supplied to the injection cavity mold 30 and the injection core mold 40, the preform 10 is immediately cooled after injection molding, and after being cooled to a temperature at which it can be released,
The molds are opened to release the preform 10.

In the mold releasing process of the preform 10, as shown in FIG. 5, the injection cavity mold 30 is first opened by, for example, descending drive while the relative positional relationship between the injection core mold 40 and the preform 10 is maintained. It had been. In addition, ascending drive of the injection core mold 40 and the injection cavity mold 3
Even if the downward driving of 0 is performed at the same time, the injection cavity mold 30 is first driven to open the mold for the following reason.

One of the reasons is that the injection cavity mold 30 is used.
While the mold opening direction is the direction of gravity, the injection core mold 4
This is because the mold opening direction of 0 is the direction opposite to the gravity direction. Furthermore, since the injection cavity mold 40 has a larger volume and a larger weight than the injection core mold 30, the equivalent weight acts in the direction of gravity, which is the mold opening direction of the injection cavity mold 30, to perform injection. The cavity mold 30 was driven to open the mold first.

Another reason is that the mold shrinkage of the preform 10 causes resistance to drive the mold opening of the injection core mold 40, whereas the injection cavity mold 30 has less resistance of that kind. .

[0007]

As described above, when the mold opening drive of the injection cavity mold 30 is first performed, as shown in FIG. 6, during the subsequent mold release drive of the injection core mold 40, Mold release failure occurred due to the preform 10 rising integrally with the core pin 44. The analysis result of the present inventor regarding this cause is as follows. (1) At the initial stage of the mold release process, as shown in FIG. 5, ambient air enters into the gap formed between the lower surface of the lip mold 20 and the upper surface of the injection cavity mold 30 in the direction of arrow A in FIG. This is because the air pressure promotes a state in which the preform 10 is in close contact with the core pin 44 side. Since the cavity surface 32 of the injection cavity mold 30 is formed with a draft taper, a gap is also created between the cavity surface 32 and the outer wall of the preform 10 to promote the above-mentioned close contact state by the air pressure. 1
It occurs in the entire region of 0 in the axial direction.

Generally, the preform 10 has a core pin 44.
It easily adheres to the side, and one of the reasons is that the preform 10
This is because the heat shrinks in the radial direction and makes close contact with the core pin 44. According to the experiments conducted by the present inventor, when the preform 10 was injection-molded from polypropylene (PP), the above-mentioned mold-releasing defects occurred more frequently than the polyethylene terephthalate (PET) preform 10. This is because the heat shrinkage rate of PP is almost 15/1000,
This is because the heat shrinkage rate of T is approximately 5/1000, which is considerably large.

Another reason why the preform 10 is likely to adhere to the core pin 44 side is that the cooling efficiency of the injection cavity mold 30 is higher than that of the injection core mold 40. This is because the contact area of the injection cavity mold 30 with the preform 10 is large. For this reason, the heat distribution in the cross section of the resin wall of the preform 10 is roughly divided into an outer skin layer, an inner skin layer and a core layer.
The outer skin layer has a relatively low temperature due to the high cooling efficiency of the injection cavity mold 30, and the outer skin layer is thicker than the inner skin layer. On the other hand, because the cooling efficiency of the injection core mold 40 is low, the temperature of the inner skin layer is considerably higher than that of the outer skin layer.
The core layer sandwiched between these two skin layers has the highest temperature. As described above, since the temperature of the inner skin layer that is in contact with the core pin 44 of the injection core mold 40 is relatively high, the preform 10 rises while being in close contact when the core pin 44 is released.

The thermal conductivity of the PP preform 10 for blow molding is 2-4 × 10 ^-4 cal / cm · sec.
-° C, which is considerably lower than the thermal conductivity of the PET preform 10 of 5.8 to 7.8 x 10 ^-4 cal / cm-sec- ° C. Therefore, the temperature of the inner skin layer of the PP preform 10 is relatively high, and
This is one of the reasons why the mold release of the preform 10 is increased. (2) The mold release failure as shown in FIG.
The body portion 14 of the preform 10 is deformed in the radial direction. However, when the injection cavity mold 30 is first driven to be released, the body portion 14 of the preform 10 cannot be prevented from being deformed in the radial direction. Is. (3) As one of mold release defects, the lip portion 12 of the preform 10 may be separated from the lip mold 20. Generally, the closed state of the lip die 20 composed of a pair of split dies 20a and 20b is performed by an urging force of a spring or the like, but in the state shown in FIG. However, since the lip mold 20 is easily driven to open, the above-described mold release failure occurs. (4) One of the reasons why the mold release of the PP preform 10 is likely to occur is that the mold release temperature is considerably higher than that of PET. PP is PE
This is because the crystallization speed is generally higher than that of T, so that if the mold release temperature is the same as that of PET, crystallization will proceed from the time of mold release and it will be difficult to stretch during blow molding. Since the mold release temperature is high, the preform 10 is likely to adhere to the core pin 44, and the above-mentioned mold release defect is likely to occur. If the mold release temperature is lowered, the cooling time must be taken sufficiently, the cycle time becomes long, and the transparency and blow characteristics of the bottle deteriorate.

The above-mentioned problems are not limited to the so-called one-stage system in which the injection molding process of the preform 10 and the subsequent blow molding process are continuously performed, but the so-called two-stage system in which the injection molding process and the blow molding process are carried out in other stages. The same applies to the stage method.

This type of mold release failure is more noticeable when the preform 10 is a so-called narrow mouth type in which the opening diameter of the lip portion 12 is relatively small with respect to the entire length of the preform 10 and the draft taper angle of the preform 10 is small. Occur in.

In the past, in order to prevent this type of mold release defect, a concavo-convex pattern was formed on the outer surface of the core pin 44, or a coating material was applied to smooth the mold release. However, the concavo-convex pattern formed on the core pin 44 remains as a streak on the inner wall surface of the final molded product, which is one of the causes of poor appearance in the case of a transparent container. Also, when applying a coating material, the durability of the coating material is limited,
Since the application must be repeated frequently, the molding cost has increased.

Therefore, an object of the present invention is to provide a mold releasing method capable of significantly reducing the mold release defect of the preform by a simple method of changing the sequence of the sequence in the mold releasing step. Especially.

[0015]

According to the present invention, a preform is molded by injecting a resin into a cavity formed by clamping an injection cavity mold and an injection core mold, and the preform is separated from each mold. When molding, in the initial stage of the mold release step, while maintaining the relative positional relationship between the preform and the injection cavity mold, the injection core mold is moved relative to the preform, and at least the The method is characterized by including the step of bringing the tip of the injection core mold into non-contact with the inner wall of the bottom of the preform.

[0016] In carrying out the above method, a lip die comprising a pair of split dies defining the outer wall of the lip portion of the preform is provided, the lip die having a tapered projection, and the injection cavity die being a die. It has a tapered hole that comes into contact with the tapered protrusion when tightening, and the tip of the injection core mold is not in contact with the inner wall of the bottom of the preform while maintaining the contact state of the tapered protrusion and the tapered hole. Is desirable.

The above method is particularly effective when the preform is injection molded from polypropylene.

[0018]

In the initial stage of the mold releasing process, the injection core mold is first moved relative to the preform while the relative positional relationship between the preform and the injection cavity mold is maintained in the state when the mold is clamped. In the initial stage of this mold release process, a gap is formed between the injection core mold and the inner wall of the preform, and air is introduced into this gap so that there is no contact between the tip of the injection core mold and the inner wall of the bottom of the preform. The resistance during driving can be reduced. Further, at this time, the cavity surface of the injection cavity mold arranged around the preform can restrict the preform from being deformed in the radial direction. Mold release failure occurs due to the maximum resistance when driving without contact between the tip of the injection core mold and the inner wall of the bottom of the preform.Preform deformation is prevented when this maximum resistance acts. As a result, the mold release defect of the preform hardly occurs thereafter.

Also in the initial stage of the mold releasing process, the opening of the lip mold is restricted by engaging the tapered protrusion of the lip mold and the tapered hole of the injection cavity mold in the same manner as at the time of mold clamping. It is also possible to prevent mold release failure in which the rib part of the preform is separated from the lip mold.

The present invention is particularly applicable to mold release of polypropylene preforms having a relatively high heat shrinkage and a relatively low heat conductivity, and in addition, the mold release temperature must be increased from the viewpoint of blow molding characteristics. It is valid. Here, polypropylene means a homopolymer of propylene and a copolymer of propylene and another α-olefin.

[0021]

EXAMPLE An example in which the method of the present invention is applied to a mold releasing process of a PET preform will be specifically described below with reference to FIGS.

FIG. 1 shows an initial stage of a mold releasing process of the preform 10, and members having the same functions as those in FIG. 4 are designated by the same reference numerals. In this example,
The injection core mold 40 is driven to rise, and the injection cavity mold 30
Is driven downward to realize the mold release process, and the position of the lip mold 20 is immovable.

What is characteristic of the method of this embodiment is that the injection core mold 40 is first driven to be released at the initial stage of the releasing process. At the initial stage of the mold release process shown in FIG. 1, the tip end surface 46 of the core pin 44 of the injection core mold 40 is
However, the core pin 44 is pulled out to a state where it is not in contact with the bottom inner wall 16 of the preform 10.

An annular taper portion 22 is formed so as to project from the lower end surface side of the lip die 22, and a taper hole 38 corresponding to this is formed in the injection cavity die 30. As shown in FIG. 4, the annular tapered portion 22 and the tapered hole 38 are in contact with each other when the molds are clamped. By ensuring this contact state, the lip mold 20 is prevented from opening in the left-right direction in FIG. This prevents the lip mold 20 from being opened left and right due to the filling pressure during the preform 10 injection process.
Even in the initial stage of the mold releasing step shown in FIG. 1, the contact state between the annular tapered portion 22 and the tapered hole 38 is secured.

FIG. 2 shows the drive timing of the injection core mold 40 and the injection cavity mold 30. As shown in the drawing, first, the injection core mold 40 is driven to be released upward, and then the injection cavity mold 3 is delayed by a time Δt.
The release driving of 0 downward is started. The time difference Δt needs to be at least 0.1 to 0.3 seconds.

After the mold release drive of the injection cavity mold 30 is started after the time difference Δt, the mold release drive of the injection core mold 40 is temporarily stopped as shown in the solid line in FIG. It may be restarted, or the release driving may be continuously performed without interruption as shown by a broken line.

FIG. 3 shows a state immediately before the release driving of the injection cavity mold 30 and the injection core mold 40 is completed. Finally, the injection cavity mold 30 is driven down to a position where the upper surface thereof is below the lower end portion of the preform 10, and the injection core mold 40 has the tip surface 4 of the core pin 44.
It is pulled out until 6 is located above the upper surface of the lip mold 20. As a result, the lip mold 20 becomes the preform 10.
With the lip portion 12 held, it can be conveyed horizontally, and can be carried into the temperature control or blow molding station in the next step.

According to the method of this embodiment, the driving for making the tip end surface 46 of the core pin 44 out of contact with the bottom inner wall 16 of the preform 10 is realized in the initial stage of the mold releasing process. At the time of pulling drive for making the tip end surface 46 of the core pin 44 out of contact with the bottom inner wall 46 of the preform 10,
The pullout resistance acting on the core pin 44 is maximum,
The mold release failure as shown in FIG. 6 does not occur for the following reasons. (1) When the injection core mold 40 is first pulled out and driven, a gap is created between the opposed surfaces of the annular tapered portion 42a of the base end portion 42 of the injection core mold 40 and the tapered hole 24 of the lip mold 20. Further, the core pin 44 of the injection core mold 40 and the inner wall surface of the preform 10 defined by the outer wall surface of the core pin 44 are each formed with a draft taper. Therefore,
By driving the injection core mold 40 upward first, a gap is also created between the core pin 44 and each tapered surface of the inner wall surface of the preform 10. In this way, since the above-mentioned gap is formed in the initial stage of the pulling drive of the injection core mold 40, air is introduced in the direction of arrow A in FIG.
Air will enter between the 0 inner walls. By introducing this air, it is possible to reduce the resistance generated at the time of driving to bring the tip end surface 46 of the core pin 44 and the bottom inner wall 16 of the preform 10 out of contact with each other.

As described above, according to the method of this embodiment, the air is introduced between the core pin 44 and the inner wall of the preform 10 at the initial stage of the mold releasing step. This is significantly different from the air introduction state (see FIG. 5) that increases the close contact state of the reform 10. (2) In order for the conventional mold release defect shown in FIG. 6 to occur, the outer wall of the preform 10 must have a degree of freedom to be deformed in the radial direction. On the other hand, in the method of this embodiment shown in FIG. 1, the preform 10 does not have the degree of freedom of deformation in the radial direction due to the cavity surface 32 of the injection cavity mold 30 when the maximum drawing resistance occurs in the core pin 44. . Therefore, even if the core pin 44 is pulled out and driven in this state, it is possible to prevent the tip end surface 46 and the bottom inner wall 16 of the preform 10 from being in close contact with each other and being driven upward together. (3) According to the method of this embodiment, the lip portion 12 of the preform 10 is prevented from falling off the lip die 20 and being driven upward together with the core pin 44 when the maximum pullout resistance acts on the core pin 44. it can. This is because the annular taper portion 22 of the lip mold 20 and the injection cavity mold 3 are also in the initial stage of this mold release process as in the mold clamped state.
This is because the contact state with the tapered hole 38 of 0 is secured. By ensuring this contact state, the pair of split molds 20
The lip mold 20 composed of a and 20b is restricted from being opened in the left-right direction in FIG.

According to the method of this embodiment, the above (1)-
Due to the reason (3), the heat shrinkage rate is higher than that of PET,
Further, even when the preform 10 made of PP having a low thermal conductivity is released from the mold, there is no mold release defect called so-called winding as shown in FIG. The mold release of the preform 10 could be realized.

Further, in the case of the PP preform 10, the mold release temperature of the preform 10 is several tens of degrees higher than that of PET (for example, 120 to 130 ° C.), and the core pin 44 and the preform 10 are likely to adhere to each other. As a condition, by adopting the method of the above-described embodiment, the preform 10 could be driven at a relatively high mold release temperature without causing mold release defects. As a result, in the subsequent blow molding step, blow molding can be performed at a temperature suitable for stretching PP, and a high quality hollow body having excellent shapeability and transparency can be molded.

In addition, since the mold release driving of the preform 10 can be performed at such a high mold release temperature, the cooling process is performed after the injection molding of the preform 10 while maintaining the mold clamping state. The time can be shortened, and especially in a so-called one-stage injection stretch blow molding apparatus in which the cycle time is determined by the processing time at the injection molding station, the cycle time can be greatly shortened.

The present invention is not limited to the above embodiment, and various modifications can be made within the scope of the gist of the present invention. In the above-described embodiment, the embodiment in which the preform 10 is injection-molded with PP is applied, but the same applies to the case where the preform 10 is injection-molded using a resin other than that. In this case, the mold release process can be realized at a temperature higher than the current mold release temperature, and the cooling time at the injection molding station can be shortened, so that a drastic reduction in cycle time can be expected. Further, the present invention is
When the pullout resistance with respect to the core pin 44 is high, that is, the lip portion 1 with respect to the axial length of the preform 10.
2 is more effective when it is a narrow mouth type having a relatively small opening diameter and a relatively small drawing taper angle, but also in the case of preforms of other shapes, the mold release defect is similarly reduced. It is possible.

In the above-mentioned embodiment, the case where the injection core mold 40 is driven to be released upward and the injection cavity mold 0 is driven to be released downward has been described as an example. Applicable. For example, in the case where the injection cavity mold 30 is fixed and the lip mold 20 and the injection core mold 40 are driven to be released upward, the lip mold 2 as in the conventional case.
0 and the injection core die 40 are not integrally driven for release, but only the injection core die 40 may be driven for release upward.

[0035]

As described above, according to the method of the present invention, the preform is pulled out together with the core pin even when the preform is released at a relatively high release temperature. It is possible to significantly reduce the mold release defects that occur. Further, since the mold release of the preform can be realized at a higher mold release temperature, the cycle time of injection molding and further the cycle time from injection to blow molding can be shortened. In addition, since the preform can be released at a blow molding temperature suitable for various resins, the quality of the blow molded hollow body can be improved.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view showing an initial stage of a mold releasing process in an example to which the present invention is applied.

FIG. 2 is a timing chart showing an injection core mold and injection cavity mold release driving timing for performing the mold release step of FIG.

FIG. 3 is a schematic cross-sectional view showing the final stage of the mold releasing process in the embodiment method shown in FIG.

FIG. 4 is a schematic cross-sectional view showing a mold clamping state in an injection molding station.

FIG. 5 is a schematic cross-sectional view showing an initial stage of a mold releasing step by a conventional method.

FIG. 6 is a schematic cross-sectional view for explaining a mold release defect caused by the conventional method shown in FIG.

[Explanation of symbols]

 10 Preform 12 Lip part 14 Body part 16 Bottom part inner wall part 20 Lip type 22 Annular taper part 30 Injection cavity type 38 Taper hole 40 Injection core type 44 Core pin 46 Tip surface

Claims (3)

[Claims] 1. A preform is molded by injecting a resin into a cavity formed by clamping of an injection cavity mold and an injection core mold, and the preform is separated from each mold by a mold release step. In the initial stage, while maintaining the relative positional relationship between the preform and the injection cavity mold, the injection core mold is moved relative to the preform, and at least the tip of the injection core mold is pushed into the preform. A method of releasing a preform, comprising a step of making no contact with the inner wall of the bottom of the reform. 2. The lip mold according to claim 1, comprising a pair of split molds defining an outer wall of the lip portion of the preform, the lip mold having tapered projections, and the injection cavity mold being a mold. It has a tapered hole that comes into contact with the tapered protrusion when tightening, and the tip of the injection core mold is not in contact with the inner wall of the bottom of the preform while maintaining the contact state of the tapered protrusion and the tapered hole. A method for releasing a preform, which is characterized in that 3. The preform releasing method according to claim 1, wherein the preform is injection-molded from polypropylene.