JPH10146879A - Production of bottle made of polyethylene terephthalate resin - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a PET bottle manufacturing method capable of well molding the bottom part of a secondary mold in a two-stage blow molding method. SOLUTION: A preform 11 is subjected to blow molding to form a primary molded bottle larger than a final product having a recessed part provided to the bottom part thereof. The primary molded bottle is heated to be freely shrunk to form a shrunk bottle 19 equipped with a recessed part 21. The shrunk bottle 19 is subjected to blow molding to form a secondary molded bottle as the final product. When the shrunk bottle 19 is mounted on a secondary mold 22, a bottom part mold 24 is moved within the secondary mold 22 and a projected part 26 is inserted into the recessed part 21 of the shrunk bottle 19 and the recessed part 21 is corrected to a predetermined position to subject the bottle 19 to blow molding. The side wall part of the leading end part of the projected part 26 has a gradient θ of 75-90 deg.. The projected part 26 is composed of a heat-resistant resin low in the coefficient of friction to a PET resin and separate from the bottom part mold 24 to be attached in a freely detachable manner.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing a polyethylene terephthalate resin bottle used for beverage containers and the like.

[0002]

2. Description of the Related Art Bottles obtained by blow-molding polyethylene terephthalate resin (hereinafter abbreviated as PET resin and bottle as PET bottle) are used as containers for soft drinks such as carbonated drinks, fruit juices and mineral water. Have been. The PET bottle is excellent in various physical properties such as strength, heat resistance, transparency, gas barrier properties, and lightness because the PET resin forming the bottle body is biaxially stretched by the blow molding and molecularly oriented. .

[0003] In order to further improve the strength and heat resistance of the PET bottle, conventionally, a PET resin preform is heated to a stretching temperature and blow molded to form a primary molded bottle having an overall shape larger than that of a final product. Is formed, and the primary molded bottle is heated and shrunk freely to obtain a shrinkable bottle having an outer diameter smaller than the final product and a height substantially equal to the final product, and then blow molding the shrinkable bottle again. Thus, a production method by a so-called two-stage blow molding method for obtaining a secondary molded bottle as a final product is known. According to the two-stage blow molding method, the pet resin is sufficiently biaxially stretched as compared with a case where a final product is obtained by a single blow molding, and excellent strength and heat resistance can be obtained.

Further, when the PET bottle is used for a container of fruit juice, mineral water or the like, it does not need to have pressure resistance unlike a container used for a carbonated beverage. it can. Therefore, the center of the flat bottom as described above is formed as a concave portion bulging into the inside of the body portion, and the flat portion on the outer peripheral side of the concave portion is set as a grounding portion, so that the PET bottle is given independence. Has been done.

[0005] Since the shape of the bottom is complicated and the amount of deformation is partly large, the two-stage blow molding method has a shape corresponding to the shape of the bottom of the final product at the bottom of the primary molded bottle. It is conceivable that a concave portion to be formed is formed in advance, and this is used as the shrinkable bottle, and then blow molded to obtain the secondary molded bottle.

However, when the primary molded bottle having the concave portion bulging inside the body corresponding to the concave portion formed at the bottom of the final product is freely shrunk under heating, each part of the primary molded bottle is reduced. Since the shrinkage of the shrinkage is not uniform, there is a disadvantage that the center of the concave portion of the shrinkage bottle does not coincide with the axis of the shrinkage bottle and the bottom cannot be formed well.

[0007]

SUMMARY OF THE INVENTION The present invention is directed to a method for producing a bottle made of polyethylene terephthalate resin which can solve the above disadvantages and can form the bottom of a secondary mold in a two-stage blow molding method. The purpose is to provide.

[0008]

In order to achieve the above object, a method for producing a bottle made of polyethylene terephthalate resin according to the present invention comprises a mouth having a threaded portion on an outer peripheral portion, and a mouth connected to the mouth. And a bottom portion forming a lower portion of the body portion. The bottom portion has a flat ground portion connected to the body portion and the body portion inside the ground portion. A method of manufacturing a polyethylene terephthalate resin bottle which is provided with a concave portion which swells in the portion and which can be self-standing by the grounding portion, wherein a heated polyethylene terephthalate resin preform is blow molded in a predetermined primary molding die. By this, a first blow molding step of forming a primary molded bottle having a bottom with a concave portion bulging in the body and having a larger overall shape than the final product, and heating the primary molded bottle By freely shrinking, a shrinking step of forming a shrinking bottle having a bottom formed with a concave portion that swells in the trunk, and a shrinking bottle heated in the shrinking step in a predetermined secondary mold. A second blow molding step of forming a secondary molded bottle as a final product by blow molding, wherein the secondary molding die includes a body molding die and a concave portion formed at the bottom of the shrinkable bottle. And a bottom mold that is movable in the body mold and has a projection that is inserted into the body mold. When the shrinkable bottle is mounted on the secondary mold, the bottom mold is attached to the secondary mold. Inside, the protrusion is inserted into a concave portion formed at the bottom of the shrinkable bottle, the concave portion is corrected to a predetermined position, and blow molding of the secondary molded bottle is performed.

According to the production method of the present invention, a preform made of pet resin is first heated to a stretching temperature and then blow molded in a predetermined primary mold to form a primary molded bottle. The primary molded bottle has a cylindrical body and a bottom forming the lower part of the body, and the bottom has a concave portion bulging into the body corresponding to the concave portion of the final product. In addition, since the primary molded bottle has an overall shape larger than the final product, the PET resin is sufficiently stretched when the primary molded bottle is freely shrunk in a later step and blow-molded again, Excellent strength and heat resistance can be obtained in the secondary molded bottle.

In the manufacturing method of the present invention, the shrinkable bottle is formed by heating the body of the primary molded bottle. The primary molded bottle has a high degree of crystallinity while the distortion during molding is released by the heating, and is freely shrunk with this, and has a shrinkage having an outer diameter smaller than the final product and a height substantially equal to the final product. A bottle is obtained. At this time, the recess formed in the bottom of the primary molded bottle is taken over by the shrink bottle in almost the same shape, and a recess that swells in the body is formed in the bottom of the shrink bottle. However, in the shrinkable bottle, since the shrinkage of the primary molded bottle is not uniform in each part, the center of the concave portion does not often coincide with the axis of the shrinkable bottle.

Then, when the shrinkable bottle heated for free shrinkage is mounted on the secondary mold while being heated, the manufacturing method according to the present invention employs the bottom mold. Is moved upward from below in the secondary mold, and the projection provided on the bottom mold is inserted into the recess of the shrinkable bottle. On the other hand, the shrinkable bottle remains heated for the free shrinkage and has some flexibility, so that when the protrusion is inserted into the recess, it corresponds to the protrusion. And the concave portion is corrected to a predetermined position coinciding with the axis of the shrinkable bottle, that is, the axis of the secondary mold. As a result, the bottom mold can be securely fitted into the recess of the shrinkable bottle. Then, with the concave portion of the shrinkable bottle fitted to the bottom mold as described above, the shrinkable bottle is blow-molded in the secondary mold to form a secondary molded bottle as a final product. By doing so, the bottom shape of the shrinkable bottle is corrected along the bottom forming die, and as described above, the bottom portion forming the lower portion of the body portion has a flat grounding portion and a concave portion that swells in the body portion. A self-standing PET bottle can be manufactured by the grounding portion.

In the manufacturing method of the present invention, the tip of the projection has a substantially truncated cone shape, and the side wall of the truncated cone has a height of 75 to 90 with respect to a plane orthogonal to the axis of the secondary mold.
It is characterized by having a 90 ° gradient. The protruding portion can be easily inserted into the recess of the shrinkable bottle by easily providing the concave portion of the shrinkable bottle to a predetermined position by providing the side wall portion of the substantially frustoconical tip with the slope. can do.

If the inclination of the side wall is greater than 90 °, it is difficult for the projection to be inserted into the recess of the shrinkable bottle, and it is difficult to make the shape of the recess of the final product a predetermined shape. Further, when the inclination of the side wall portion is less than 75 °, it becomes easy for the protrusion to be inserted into the recess of the shrinkable bottle,
It is difficult to correct the position of the concave portion of the shrink bottle.

Further, in the manufacturing method of the present invention, the protrusion is made of a heat-resistant resin having a small coefficient of friction with respect to polyethylene terephthalate resin. Since the protrusion is made of a heat-resistant resin having a small coefficient of friction with pet resin, when the bottom mold is moved as described above,
Even if the center of the recess of the shrink bottle is slightly off the axis of the shrink bottle, it can slide into the recess and be inserted into the recess of the shrink bottle.

As the heat-resistant resin forming the projection, for example, a fluororesin having a small coefficient of friction with pet resin can be used.

In the manufacturing method of the present invention, the protrusion may be formed by coating the bottom mold with the heat-resistant resin, but preferably, the protrusion is formed of the heat-resistant resin. , And is detachably attached to the bottom mold.

Even if the projection is made of a heat-resistant resin, if it is used repeatedly, it gradually deteriorates and deforms due to contact with the shrinkable bottle under heating for blow molding. Therefore, the protrusions are formed separately from the bottom bottom forming die, and are detachably attached to the bottom forming die. Can be exchanged. A mold for blow molding is usually very expensive, but according to the manufacturing method of the present invention, when the protrusion is deteriorated and deformed as described above, only the protrusion needs to be replaced, and the mold is not required. Since it is not necessary to replace the whole, the effect of reducing the manufacturing cost of the PET bottle can also be obtained.

[0018]

Next, embodiments of the present invention will be described in more detail with reference to the accompanying drawings. FIG. 1 is a perspective view showing an example of a polyethylene terephthalate resin bottle obtained by the manufacturing method of the present invention, and FIGS. 2 to 6 are explanatory sectional views showing the steps of manufacturing the PET bottle shown in FIG. FIG. 7 is an enlarged sectional view showing a protrusion attached to the bottom mold shown in FIGS. 5 and 6.

As shown in FIG. 1, a plastic bottle 1 according to the present embodiment has a mouth portion 3 provided with a screw portion 2 on the outer peripheral portion, and a body portion formed below the mouth portion 3 so as to be continuous with the mouth portion 3. 4 and a bottom 5 forming the lower part of the body 4. The body 4 is biaxially stretched by blow molding, and has a substantially rectangular cross section. Further, a predetermined design shape is formed on the side surface 6 of the body 4 by blow molding.

On the other hand, the bottom 5 is provided with a flat ground portion 7 connected to the body portion 4 and a concave portion 8 bulging into a frustoconical shape inside the body portion 4 inside the ground portion 7. And PET bottle 1
Is formed to be self-supporting by the grounding portion 7.

Next, a method of manufacturing the plastic bottle 1 shown in FIG. 1 will be described.

First, as shown in FIG. 2, a preform 11 obtained by injection molding of pet resin is heated at 95 to 100 ° C.
, And the mouth 3 is held by the mandrel 12 to provide a cavity having a shape conforming to the outer shape of the primary molding bottle, and the primary molding metal comprising the body molding die 14 and the bottom molding die 15. Attach to the mold 13. The mouth 3 of the preform 11 may be previously whitened and crystallized by heating.

Next, as shown in FIG. 3, a stretch rod 16 is inserted into the inside of the preform 11, and the preform 11 is stretched in the longitudinal direction by the stretch rod 16 while the preform 11 is inserted through the mouth 3. 20-25 in 11
The first blow molding is performed by introducing high-pressure air of kg / cm ² . As a result, the preform 11 is expanded into a shape following the internal shape of the primary molding die 13, and a primary molded bottle 17 whose overall shape is larger than the PET bottle 1 shown in FIG. 1 as a final product is formed. You. Further, a flat portion 17b connected to the body portion 17a and a body portion 17 inside the flat portion 17b correspond to the ground portion 7 and the concave portion 8 of the plastic bottle 1 shown in FIG.
A concave portion 17c that protrudes in a truncated cone shape is formed in a.

Next, the primary molding bottle 17 is taken out and moved to a heating furnace. As shown in FIG. 4, the heating furnace has a plurality of infrared panel heaters 18a arranged on one side of the body 17a of the primary molding bottle 17 so as to face the body 17a, and a reflection plate on the other side. 18b are arranged.

While the mouth 3 of the primary molding bottle 17 is held by the mandrel 12, while rotating the primary molding bottle 17, the body 17a is heated by the infrared panel heater 18a so that the surface of the body 17a has a maximum of 180 Heated to about ° C.

When the primary molded bottle 17 is heated as described above, the strain at the time of the first blow molding shown in FIG. 3 is released, while the density is increased and the whole is shrunk, and the final product is shrunk. A shrink bottle 19 having a smaller outer diameter and a height approximately equal to the final product is formed. At this time, the shrink bottle 19
The flat portion 17b and the concave portion 17c formed at the bottom of the primary molded bottle 17 are inherited in almost the same shape at the bottom of the primary molded bottle 17, and the flat portion 20 connected to the trunk of the shrinkable bottle 19 and the flat portion 20 A concave portion 21 bulging like a truncated cone is formed inside the body portion inside. However, since the shrinkage of the primary molded bottle 17 is not uniform at each part, the center of the concave portion 21 is formed off the axis A of the shrinkable bottle 19.

Next, as shown in FIG. 5, the shrinkable bottle 19 is mounted in a secondary molding die 22 having a cavity having a shape corresponding to the external shape of the PET bottle 1 as the final product. At this time, the shrink bottle 19 has just been heated by the infrared panel heater 18a, and the temperature is about 160 ° C.

The secondary molding die 22 includes a body molding die 23a,
23b and a bottom mold 24. The bottom mold 24 further includes a mold body 25 and a shrink bottle 1
9 and a projection 26 inserted into the recess 21 of the ninth embodiment. The molding die body 25 is movable in the direction of the axis A in the secondary molding die 22. The protrusion 26 is made of a fluororesin such as polytetrafluoroethylene or the like.
It is configured as a separate body that is removable. The polytetrafluoroethylene has a low coefficient of friction with pet resin, has a melting point of 327 ° C., and has excellent heat resistance. The shape of the projection 26 will be described later in detail.

When the shrink bottle 19 is mounted on the secondary molding die 22, the shrink bottle 19 is first moved to a predetermined position, and then the bottom molding die 24 is moved into the secondary molding die 22. Move in the direction. Then, as shown in FIG. 6, the protrusion 26 attached to the molding die body 25 slides into the concave portion 21 of the shrinkable bottle 19, and immediately after being heated by the infrared panel heater 18a as described above. The shrinkable bottle 19 that retains flexibility is the protrusion 2
6 and is corrected so that the position of the concave portion 21 coincides with the axis A of the shrinkable bottle 19. As a result, the bottom mold 24 is fitted to the bottom of the shrinkable bottle 19 as shown in FIGS.

Then, by closing the body forming dies 23a and 23b so as to sandwich the shrink bottle 19, the shrink bottle 19 is mounted on the secondary forming die 22.

Next, in this state, second blow molding is performed by introducing high-pressure air of 35 to 40 kg / cm ² into the shrinkable bottle 19 from the mouth portion 3. By the second blow molding, the shrinkable bottle 19 is expanded into a shape along the internal shape of the secondary molding die 22, and the secondary molding bottle 27 is formed. At this time, the flat portion 20 at the bottom of the shrink bottle 19
Is the grounding portion 7 of the plastic bottle 1, and the concave portion 21 of the shrinkable bottle 19 is the concave portion 8 of the plastic bottle 1. The temperature of the secondary molding die 22 is set at 130 to 140 ° C., and the secondary molding bottle 27 is heat-set.

Then, after cooling, the secondary molding die 22
Is opened and the secondary molded bottle 27 is taken out to obtain the PET bottle 1 as a final product.

Next, the detailed shape of the projection 26 attached to the molding die body 25 of the bottom molding die 24 will be described.

The protruding portion 26 has a circular shape in plan view, and as shown in FIG.
1, a substantially frusto-conical tip portion 32 is provided. Also,
A fitting portion 33 is provided below the central portion for fitting and attaching to the molding die body 25, and a hole portion 34 for receiving a trace of the gate of the shrinkable bottle 19 is provided above the central portion. The hole 33 communicates with the hole 33.
The hole 34 has a tapered surface that is inclined downward at the center.

The side wall 36 of the tip 32 has an angle θ of 75 to 90 ° with respect to a plane orthogonal to the axis A of the secondary mold 22.
With a gradient of As shown in FIG. 6, the protrusion 26 has a slope in the side wall portion 36, as shown in FIG. 6.
It is possible to easily slide into the concave portion 21 of the shrinkable bottle 19 and insert it, and the position of the concave portion 21 can be easily corrected.

[Brief description of the drawings]

FIG. 1 is a perspective view showing an example of a polyethylene terephthalate resin bottle obtained by a production method of the present invention.

FIG. 2 is an explanatory sectional view showing a first blow molding step of the manufacturing method of the present invention.

FIG. 3 is an explanatory sectional view showing a first blow molding step of the manufacturing method of the present invention.

FIG. 4 is an explanatory sectional view showing a shrinking step of the manufacturing method of the present invention.

FIG. 5 is an explanatory sectional view showing a second blow molding step of the manufacturing method of the present invention.

FIG. 6 is an explanatory sectional view showing a second blow molding step of the manufacturing method of the present invention.

FIG. 7 is an enlarged sectional view showing a projection attached to the bottom mold shown in FIGS. 5 and 6;

[Explanation of symbols]

1 ... bottle made of polyethylene terephthalate resin, 2 ...
Screw part, 3 ... Mouth part, 4 ... Body part, 5 ... Bottom part, 7 ... Ground part, 8 ... Concave part, 11 ... Preform, 17 ... Primary molded bottle, 19 ... Shrinkage bottle, 24 ... Bottom mold, 26 ... Projection part, 27 ... Secondary molded bottle, 32
... tip, 36 ... side wall, θ ... gradient.

Claims (4)

[Claims] 1. A mouth having a threaded portion on an outer periphery thereof, a biaxially stretched body formed below the mouth connected to the mouth, and a bottom part forming a lower portion of the body. The bottom portion comprises a flat ground portion connected to the body portion, and a concave portion bulging into the body portion inside the ground portion, and a method for manufacturing a polyethylene terephthalate resin bottle capable of being self-standing by the ground portion By blowing a heated polyethylene terephthalate resin preform in a predetermined primary mold, a bottom portion having a concave portion bulging in the body is provided, and the overall shape is smaller than that of the final product. Blow molding step of forming a large primary molded bottle, and forming a shrinkable bottle having a bottom portion formed with a concave portion that swells in a body by heating the primary molded bottle to freely shrink. Shrinking process A second blow molding step of forming a secondary molded bottle as a final product by blow molding the shrinkable bottle heated in the shrinking step in a predetermined secondary molding die. The next mold includes a body mold, and a bottom mold that includes a protrusion inserted into a recess formed in the bottom of the shrink bottle and is movable in the body mold. When mounted on the secondary mold, the bottom mold is moved in the secondary mold, and the projection is inserted into a recess formed in the bottom of the shrinkable bottle, and the recess is positioned at a predetermined position. A method of manufacturing a bottle made of polyethylene terephthalate resin, comprising straightening and blow-molding the secondary molded bottle. 2. The protruding portion has a substantially frusto-conical end portion, and the frusto-conical side wall has a slope of 75 to 90 ° with respect to a plane perpendicular to the axis of the secondary mold. The method for producing a polyethylene terephthalate resin bottle according to claim 1, further comprising: 3. The production of a polyethylene terephthalate resin bottle according to claim 1, wherein the protrusion is made of a heat-resistant resin having a small friction coefficient with respect to the polyethylene terephthalate resin. Method. 4. The polyethylene terephthalate according to claim 3, wherein said projection is formed separately from said bottom molding die by said heat-resistant resin, and is detachably attached to said bottom molding die. Manufacturing method of resin bottle.