JPH10146880A - Production of bottle made of polyethylene terephthalate resin - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a PET bottle prevented from the core shift of a bottle bottom part and capable of obtaining excellent self-stability by two-stage blow molding. SOLUTION: A preform 11 is subjected to blow molding to form a primary molded bottle 17 equipped with a body part 17a and a bottom part 17b, characterized by that the bottom part 17b is equipped with flat parts 29, 30 and a central part 31 protrudes into the bottom part 17a and larger than a final product. The body part 17a is heated to be freely shrunk to form a shrunk bottle 19 equipped with a flat earth part 20 and the recessed part 21 expanded into the body part inside the earth part 20. The shrunk bottle 19 is subjected to blow molding to form a secondary molded bottle 26 as the final product. Blow molding is performed so that the ratio r2 /r1 of the outer diameter r1 of the bottom part 17b of the primary molded bottle 17 to the outer diameter r2 of the max. part connected to the bottom part 17b of the body part 17a rising from the outer periphery of the flat part 30 becomes 1.1-1.8, pref., 1.3-1.6. The flat parts 29, 30 are taper parts inclined toward the center of the bottom part 17b.

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, the primary molded bottle is heated and freely shrunk to obtain a shrinkable bottle, and then the shrinkable bottle is blow-molded again,
A manufacturing 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 crystallization of the body of the PET bottle is more advanced than in the case where the final product is obtained by one blow molding,
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 portion is complicated and the amount of deformation is partially large, the bottom shape is formed at the bottom of the primary molded bottle and at the bottom of the final product in the two-stage blow molding method. It is conceivable that a concave portion and a flat portion corresponding to the concave portion and the ground portion are formed in advance, and this is corrected at the time of blow molding as the shrinkable bottle to form the secondary molded bottle. In this case, when the primary molded bottle is shrunk under heating to form a shrinkable bottle, a shrinkable bottle having a concave portion similar to the concave portion formed at the bottom of the primary molded bottle at the bottom is obtained. Next, when the shrinkable bottle is blow-molded, if a blow molding is performed using a bottom mold that fits into the concave portion, it is expected that a secondary molded bottle having the bottom shape can be easily obtained.

[0006] However, a bulging recess is formed in the body corresponding to the recess formed in the bottom of the final product, and the primary molded bottle having a flat portion formed on the outer peripheral side of the recess is heated. When freely shrinking downward, in the partial region continuing from the flat portion to the body portion, the shrinkage bottle does not shrink uniformly in the circumferential direction. There is a disadvantage that the bottle becomes a so-called misaligned bottle whose center is shifted. In such a misalignment bottle, misalignment is not corrected even in blow molding for obtaining a secondary molded bottle, and misalignment also occurs at the bottom of a PET bottle as a final product. The misalignment at the bottom of the bottle of the final product not only lowers the commercial value as poor appearance, but also causes uneven thickness, which is not preferable.

Further, when the primary molded bottle is freely shrunk under heating, the shrinkage from the flat portion to the portion connected to the body is larger than the flat portion. There is also the inconvenience of forming a part. This annular projection is not uniform in the projection direction, height, etc., and is not corrected even in blow molding to obtain a secondary molded bottle, similarly to the misalignment, so that the self-standing stability of the bottle of the final product is lost. There are cases.

[0008]

SUMMARY OF THE INVENTION The present invention solves such inconveniences, and can prevent the misalignment at the bottom of the bottle of the final product by the two-stage blow molding method, and provide excellent self-standing stability. It is an object of the present invention to provide a method for producing a polyethylene terephthalate resin bottle that can be used.

[0009]

Means for Solving the Problems The present inventors have formed a swelled recess inside the body corresponding to the recess formed at the bottom of the final product, and formed an outer peripheral side of the recess. The cause of the misalignment and the occurrence of the annular protrusion in a shrinkable bottle obtained by freely shrinking a primary molded bottle having a flat portion formed thereon under heating was examined. As a result, the present inventors have found that the temperature distribution of the preform itself and the stretching ratio of the primary molded bottle when stretch blown from the preform are different in each part of the bottle, and particularly, the fluctuation of the stretching ratio is caused by the change in the body of the primary molded bottle. This is remarkable in a portion extending from the lower portion to the bottom portion having a concave portion that protrudes inside the body portion.When such a primary molding bottle is freely shrunk under heating, the region extending from the flat portion to the body portion is individually reduced. Showed a shrinkage behavior in accordance with the stretching ratio, and it was found that the above-described misalignment and annular protrusion occurred.

The stretch ratio of the primary molded bottle will be described in detail. In the primary molded bottle, a thick, unstretched portion is formed at the center of the bottom, and the flat portion at the bottom is close to the central portion of the bottom. Has become a low part. On the other hand, the part that continues from the flat part to the trunk is a part with a high stretching ratio. As a result, the region extending from the flat portion to the body portion corresponds to a portion where the stretching ratio rapidly changes from a low ratio to a high ratio, and this portion shows the shrinkage behavior due to a change in the stretching ratio during blow molding. It is considered something.

Therefore, the present inventors have further studied and found that when a primary molded bottle is blow-molded, a flat portion is provided on a bottom portion forming a lower portion of the cylindrical body portion and a portion connected to the body portion. in primary molding bottle central portion of at least the bottom portion is overhanging in the body portion, the ratio to the outer diameter r ₂ of the maximum portion connected to said bottom of the body portion rising from the outer periphery of the flat portion of the outer diameter r ₁ of the bottom portion It has been found that by performing blow molding so that r ₂ / r ₁ is in a specific range, a shrinkable bottle free from the above-described misalignment and annular protrusions can be obtained even when freely shrunk under heating. Reached.

Therefore, in the method for producing a polyethylene terephthalate resin bottle according to the present invention, a biaxially stretched portion formed with a screw portion on the outer peripheral portion and formed below the mouth portion following the mouth portion. A torso portion and a bottom portion forming a lower portion of the torso portion, the bottom portion including a flat ground portion connected to the torso portion and a concave portion bulging into the body portion inside the ground portion, A method for producing a polyethylene terephthalate resin bottle capable of self-supporting by a part, wherein a polyethylene terephthalate resin preform is heated to a stretching temperature, and then blow-molded in a predetermined primary mold to form a cylindrical body. A bottom portion forming a lower portion of the body portion, the bottom portion having a flat portion at a portion connected to the body portion, and at least a central portion of the bottom portion projecting into the body portion, and the overall shape is smaller than that of the final product. A first blow molding step for forming a large primary molded bottle, and heating and freely shrinking the trunk of the primary molded bottle, thereby forming a flat portion in a portion connected to the bottom trunk, and A shrinking step of forming a shrinkable bottle in which a concave portion that swells in the body inside the body is formed, and a shrinkage bottle is formed by a predetermined shank forming mold and a bottom mold that is fitted to the bottom of the shrinkable bottle. And a second blow molding step of forming a secondary molded bottle as a final product by blow molding in a secondary mold, wherein the first blow molding step comprises: The ratio r ₂ / r ₁ of the outer diameter r ₂ of the largest part of the body part rising from the outer periphery of the flat part with the outer diameter r ₁ at the bottom of the molded bottle to the bottom is preferably in the range of 1.1 to 1.8. Is in the range of 1.3 to 1.6 Wherein the blow molding so that.

According to the manufacturing method of the present invention, first, a preform made of PET resin is heated to a stretching temperature and then blow molded in a predetermined mold to form a primary molded bottle. The primary molded bottle includes a cylindrical body and a bottom forming a lower portion of the body, and the bottom includes a flat portion in a portion connected to the body and at least a central portion of the bottom is provided in the body. It has an overhanging shape, and the overall shape is larger than the final product. In this way, by making the overall shape of the primary molded bottle larger than the final product, when the primary molded bottle is freely shrunk in the subsequent process and blow molded again, the crystallinity of the pet resin advances, Excellent strength and heat resistance are exhibited 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. Due to the heating, the distortion of the primary molded bottle is released and the degree of crystallinity is increased, and the primary molded bottle is freely shrunk.

[0015] In the manufacturing method of the present invention, the primary molded bottle is provided with a ratio r ₂ / r of an outer diameter r ₁ of a bottom portion of the body portion rising from the outer periphery of the flat portion to an outer diameter r ₂ of a maximum portion connected to the bottom portion. by r ₁ is kept by blow molding to be in the range of 1.1 to 1.8, by the free shrink, leading to body portion of the bottom portion of the contraction bottle from the outer side of the flat portion of the primary molded bottles A flat portion is formed in the portion, and a concave portion that swells into the body of the shrinkable bottle is formed inside the flat portion of the shrinkable bottle from the inner peripheral side of the flat portion of the primary molded bottle and the center of the bottom. You. And the flat part of the said shrink bottle does not produce the deformation | transformation which inverts and protrudes outward.

Then, the bottom of the shrinkable bottle is fitted into the bottom mold of the secondary mold, and blow-molded in the secondary mold to provide a flat grounding portion, and It is possible to form a secondary molded bottle as a final product having excellent stability.

When the value of the ratio r ₂ / r ₁ is larger than 1.8, when the primary molded bottle is freely shrunk under heating,
The flat portion of the shrinkable bottle inverts and protrudes outward from the bottle around the recess, and the recess is displaced from the central axis of the bottle, thereby impairing the self-supporting stability of the final product.
If the value of the ratio r ₂ / r ₁ is less than 1.1, the portion where the bottom of the primary molded bottle is connected to the body cannot be molded well.

The primary molded bottle has a ratio r ₂ / r ₁ of 1.3 to the outer diameter r ₂ of the largest part of the body part rising from the outer periphery of the flat part with the outer diameter r ₁ of the bottom part connected to the bottom part. By performing blow molding so as to fall within the range of 1.6 to 1.6, in the case of the free shrinkage, the flat portion of the shrinkable bottle is reliably prevented from protruding outward, and the recess is formed on the center axis of the bottle. Can be reliably maintained.

When the value of the ratio r ₂ / r ₁ is larger than 1.6, when the primary molded bottle is freely shrunk under heating, the flat portion of the shrinkable bottle is located outside the bottle around the recess. In some cases, the convex portion may be inverted and the concave portion may be displaced from the central axis of the bottle. When the concave portion is less than 1.3, it is difficult to form a portion where the bottom of the primary molded bottle is continuous with the body.

Further, in the manufacturing method of the present invention, the flat portion of the primary molded bottle is a tapered portion inclined toward the center of the bottom. By making the flat portion of the primary molded bottle the tapered portion, at the time of the free shrinkage, the central portion of the bottom of the primary molded bottle is surely swelled into the body of the shrinkable bottle to reduce the concave portion. In addition to being formed, the deformation of the flat portion of the shrinkable bottle projecting outward can be reliably prevented.

[0021]

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. 7A is an enlarged view of a main part comparing the bottom shapes of the primary molded bottle and the shrinkable bottle shown in FIG. 4, and FIG. 7B is an essential part of a conventional primary molded bottle and a shrinkable bottle. It is explanatory sectional drawing which compares a bottom part shape by enlarging.

As shown in FIG. 1, a plastic bottle 1 according to the present embodiment has a mouth portion 3 having a screw portion 2 on an 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 portion 5 has a flat ground portion 7 connected to the body portion 4 and a concave portion 8 bulging into the body portion 4 inside the ground portion 7.
And Then, the plastic bottle 1 is
It is formed so that it can be independent.

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 a pet resin was heated at 95 to 100 ° C.
, And the mouth portion 3 is held by the mandrel 12 and attached to the primary molding die 13 having a cavity having a shape corresponding to the external shape of the primary molding bottle. Primary molding die 1
3 comprises a body forming die 14 and a bottom forming die 15.
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 along the internal shape of the primary molding die 13, and the primary molded bottle 17 is formed. The primary molded bottle 17 is
It has a bottom shape described later, and the overall shape is larger than the PET bottle 1 shown in FIG. 1 which is a final product.

Next, the primary molding bottle 17 is moved to a heating furnace. The heating furnace, as shown in FIG.
A plurality of infrared panel heaters 18a are arranged so as to face the body 17a, and a reflection plate 18b is provided on the other side.
Is arranged.

Then, with the mouth 3 of the primary molding bottle 17 held by the mandrel 12, the body 17a is heated by the infrared panel heater 18a while rotating the primary molding bottle 17. At this time, the temperature of the infrared panel heater 18a is about 500 ° C., whereby the surface of the body 17a of the primary molding bottle 17 is heated to a maximum of about 180 ° C.

When the primary molding bottle 17 is heated as described above, the distortion at the time of the first blow molding shown in FIG. 3 is released, while the crystallinity increases, and the primary molding bottle 17 shrinks as a whole. A shrink bottle 19 having an outer diameter smaller than the final product and a height substantially equal to the final product is formed. At this time, the bottom portion 17b of the primary molded bottle 17 is contracted, and a flat portion 20 is formed from the outer peripheral side of the flat portion of the bottom portion 17b to the portion connected to the bottom trunk portion of the shrinkable bottle 19. In addition, the bottom 1 of the primary molded bottle 17
A recess 21 bulging into the body of the shrinkable bottle 19 is formed inside the flattened portion 20 of the shrinkable bottle 19 from the inner peripheral side of the flat portion 7b and the center of the bottom portion 17b.

Next, as shown in FIG. 5, the shrinkable bottle 19 is mounted on 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 is composed of a body molding die 23 and a bottom molding die 24. The bottom molding die 24 has a protruding portion 25 fitted into the recess 21 of the shrinkable bottle 19. It is provided movably in the direction of the axis A of the mold 22.
Although the shrinkage bottle 19 freely shrinks as described above, since the center of the concave portion 21 freely shrinks the primary molding bottle 17, it shrinks in accordance with the axis of the secondary molding die 22. Next, as the bottom molding die 24 moves inward of the secondary molding die 22, the protrusion 25 is fitted into the concave portion 21 as shown in FIG.

Next, the shrinkable bottle 19 is mounted on the secondary mold 22 as described above, and the shrinkable bottle 1 is inserted through the mouth 3 while the protrusion 25 of the bottom mold 24 is fitted in the recess 21.
The second blow molding is performed by introducing high-pressure air of 35 to 40 kg / cm ² into 9. 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 26 is formed. At this time, the flat portion 20 at the bottom of the shrink bottle 19 becomes the ground portion 7 of the plastic bottle 1, and the recess 21 of the shrink bottle 19 becomes the recess 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 26 is subjected to heat setting.

After cooling, the secondary molding die 22
Is opened and the secondary molded bottle 26 is taken out to obtain the PET bottle 1 as a final product.

In the manufacturing method of the present invention, as shown in FIG.
When molding the primary molded bottle 17 from the preform 11, blow molding is performed so that the bottom 17b has a specific shape. As shown in FIG. 7A, the bottom portion 17b includes an annular rib 27 protruding into the body portion 17a around the axis A, and a body portion 17a.
And an annular rib 28 projecting outward. Annular rib 2
7 and 28, a flat portion 29 and an outer peripheral side of the annular rib 28 are a flat portion 30.
b, forming a tapered portion inclined toward the center of the bottom 1
The central portion 31 of 7b projects into the body 17a. The trunk 17a rises from the outer periphery of the flat portion 30 at a substantially right angle.

Then, in the primary molded bottle 17, the bottom 1
The trunk portion 17 rising from the flat portion 30 having an outer diameter r ₁ of 7b.
The ratio r ₂ / r _{1 of the} largest portion connected to the bottom portion 17b with respect to the outer diameter r ₂ is in the range of 1.1 to 1.8, preferably 1.
The range is from 3 to 1.6.

By setting the value of the ratio r ₂ / r ₁ within the above range, when the primary molded bottle 17 is freely shrunk under heating as shown in FIG. a) As shown in the drawing, the flat portion 30 of the primary molding bottle 17 forms a flat portion 20 at a portion connected to the body at the bottom of the shrinkable bottle 19. In addition, primary molded bottle 1
The flat part 29 of 7 and the central part 31 of the bottom part 17 b form a concave part 21 bulging into the body of the shrinkable bottle 19 on the inner peripheral side of the flat part 20.

In the shrink bottle 19, the flat portion 20 does not protrude outside the shrink bottle 19, and the recess 21 is
, The flat grounded portion 7 can be formed in the secondary molded bottle 26 (the PET bottle 1) as the final product, and excellent self-standing stability can be obtained.

Conventionally, with respect to the production method of the present invention,
As shown in FIG. 7B, the primary molded bottle 41 is
1a and a bottom portion 41b forming a lower portion of the body portion 41a, and the bottom portion 41b is a flat portion 42 connected to the body portion 41a.
And a concave portion 43 formed on the inner peripheral side of the flat portion 42 and bulging into the body portion 41a. Then, in the conventional primary molded bottles 41, the outer diameter r ₁ of the bottom portion 41b, the ratio r ₂ / r ₁ to the outer diameter r ₂ of the maximum portion continuous to the bottom portion 41b of the body portion 41a which rises from the flat portion 42, 1. Greater than 8,
For example, it is set to 2.0.

When the primary molded bottle 41 having the above-mentioned shape is freely shrunk under heating as shown in FIG. 4 to form a shrinkable bottle 44, the concave portion 43 remains as it is, and the concave portion 43 is formed by the flat portion 42 of the primary molded bottle 41. A flat portion 45 is formed in a non-uniform shape in the circumferential direction. But,
On the inner peripheral side of the flat portion 45 and around the concave portion 43, an annular protruding portion 46 that protrudes outwardly and inverts from the center axis is formed. The shrink bottle 44 is a primary molded bottle 4
1 can be obtained by free shrinkage under heating,
The projecting direction, height and the like of the annular projecting portion 46 are not uniform, and furthermore, as shown in FIGS.
Even after the second blow molding of 4 is performed, it remains uncorrected, so that the self-standing stability of the final product is significantly impaired.

[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.

7 (a) is an enlarged view of a main part comparing the bottom shapes of the primary molded bottle and the shrinkable bottle shown in FIG. 4, and FIG. 7 (b) is an essential part of a conventional primary molded bottle and a shrinkable bottle. Explanatory sectional view which expands and compares a bottom part shape.

[Explanation of symbols]

1 ... bottle made of polyethylene terephthalate resin, 2 ...
Screw part, 3 ... mouth part, 4 ... trunk part, 5 ... bottom part, 7 ... ground part, 8 ... concave part, 11 ... preform, 17 ... primary molded bottle, 19 ... shrinkable bottle, 26 ... secondary molded bottle.

Claims (3)

[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 heating a polyethylene terephthalate resin preform to a stretching temperature, and then blow molding in a predetermined primary mold, comprising a cylindrical body portion and a bottom portion forming a lower portion of the body portion, A first blow molding for forming a primary molded bottle in which the bottom portion has a flat portion at a portion connected to the body portion and at least a central portion of the bottom portion projects into the body portion, and the overall shape is larger than a final product; Process and the primary composition By heating and freely shrinking the body of the bottle, a flat part is formed in a portion connected to the body at the bottom, and a shrinkable bottle in which a concave portion swelling in the body is formed inside the flat part. Shrinking step of forming; and blow molding the shrinkable bottle in a secondary mold consisting of a predetermined body mold and a bottom mold fitted to the bottom of the shrink bottle to form a final product. A second blow molding step of forming a next molded bottle, wherein the first blow molded step comprises a step of, using the molding die, rising from an outer periphery of the flat portion having an outer diameter r ₁ at a bottom of the primary molded bottle. Outer diameter r _{2 of the} largest part connected to the bottom of the part
Polyethylene terephthalate resin bottle manufacturing method of the ratio r ₂ / r _1, characterized in that the blow molding to be in the range of 1.1 to 1.8 relative to. Wherein said first blow molding step, by the mold, the outer diameter of the largest portion connected to said bottom of the body portion rising from the outer periphery of the flat portion of the outer diameter r ₁ of the bottom of the primary molded bottles polyethylene terephthalate resin bottle manufacturing method according to claim 1, wherein the ratio r ₂ / r ₁ for r ₂ is in the range of 1.3 to 1.6. 3. The method for producing a polyethylene terephthalate resin bottle according to claim 1, wherein the flat portion of the primary molded bottle is a tapered portion inclined toward the center of the bottom.