JP3102457B2 - Method for producing a biaxially stretched blow container with reinforced bottom - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a biaxially stretched blow container, and more particularly, to a method for producing a biaxially stretched blow container having excellent heat resistance, pressure resistance or heat and pressure resistance, and particularly having a reinforced bottom. About the method.

[0002]

2. Description of the Related Art A biaxially stretched plastic bottle withstands a heat treatment for filling a high-temperature liquid or sterilizing the contents, a heat-resistant container having a concave bottom, and a container having a self-generating pressure containing carbon dioxide gas. It is classified into a pressure-resistant container suitable for a product, a container having a self-generated pressure, and a heat-resistant container capable of withstanding heat treatment, and is required to have heat resistance, pressure resistance, and heat pressure resistance, respectively. In the heat-resistant container, blow molding and heating the molded product to crystallize,
A one-stage blow molding method in which so-called heat setting (thermal fixing) is performed in one mold is usually employed. In this one-step blow molding method, it is usually difficult to heat-set the concave bottom of the molded product by heating, and in order to guarantee heat resistance, the bottom concave has to be thick and has a complicated shape. Therefore, the basis weight of the bottom had to be increased. Also, in the case of pressure-resistant and heat-resistant pressure containers, attempts have been made to make the bottom of the container relatively deep concave in order to provide pressure resistance and self-sustainability. When a container having this bottom is formed by a single blow molding, there is a problem that the thickness of the concave vertical portion of the concave bottom portion and the vicinity of the corner portion of the lowest bottom portion connected thereto become too thin, and good pressure resistance is obtained. Therefore, the weight per unit area had to be significantly increased.

On the other hand, as a method for manufacturing a heat-resistant container, a step of primary blow molding a preform molded product using a mold,
The obtained molded product is subjected to a so-called heat setting (heat setting) process in which the molded product is heated and shrunk in an oven to shrink and crystallize. A two-stage blow molding method comprising a step of shaping is known. In this two-stage blow molding method, the primary blow molding step is to sufficiently stretch at a stretching ratio of about 2 to 6 times, and the stretched secondary molded article is sufficiently shrunk to about 60 to 90% by a heat setting step. Accordingly, the rigidity of the bottle can be improved, and heat resistance can be imparted by an intermediate heating method, so that the method is suitable as a method for manufacturing a heat-resistant container.

[0004] As an example of adopting such a two-stage blow molding method, for example, in JP-A-3-205124, a secondary molded product having a hemispherical bottom is prepared by primary blow molding, and then an oven is used. It is described that after the whole is heated, it is subjected to secondary blow molding to obtain a final molded product having a shape in which the center of the bottom is depressed inward of the container. Also, JP-A-63-18
In No. 9224, a secondary molded product having a hemispherical bottom is formed by primary blow molding, and then a tertiary molded product having a bottom shape in which the bottom is inverted and the center is recessed inward of the container is formed. It describes that the entire tertiary molded product is relatively uniformly heated and shrink-deformed, followed by secondary blow molding to obtain a final molded product.

[0005]

However, in the conventional two-stage blow molding method, if there is a portion having a large stretching ratio in the final secondary blow molding step, the portion is locally thinned and the strength is reduced. And the crystallinity is lowered, so that heat resistance cannot be obtained. That is, in the prior art described above, in the former, when the secondary blow the secondary molded product having a hemispherical bottom at the bottom into a concave final shape in which the bottom is concave inward, the stretching ratio of the bottom corner becomes large, There is a problem that the corner portion is thinned and the degree of crystallinity is reduced, and the strength and heat resistance of the portion are reduced.

Further, as in the latter case, when a secondary molded product having a hemispherical bottom shape formed by primary blow molding and having an inwardly concave bottom shape is formed by reversing the shape, the entirety of the secondary molded product is reduced. It is necessary to relatively uniformly heat and shrink its height below the size of the secondary blow mold, and at this time, a phenomenon occurs in which the trunk diameter shrinks too much more than the final shape. When performing the secondary blow molding of the heat-molded product, there is a problem that the stretch processing rate particularly at the bottom corner becomes large, and as a result, the heat resistance and strength of the portion are not sufficient as described above.

Further, when a heat-resistant container having a concave shape and a concave portion having a thick bottom is formed by a two-stage blow molding method, the bottom of a secondary molded product usually formed by primary blow molding is the same as the final product. If the bottom is heated in the same manner as the body, the thick portion having a large heat capacity usually has a slow temperature rise, and the portion excluding the bottom thick portion is particularly heated. When such a heated secondary molded article is subjected to secondary blow molding, only the high-temperature thin portion is stretched, and particularly the bottom corner portion is extremely thin, which is not preferable. Further, even when the thick portion at the bottom is to be selectively heated, the thick portion having a low elongation ratio is whitened in a part of blow molding. Therefore, usually adopting a complicated heating method that mainly heats and shrinks the body to crystallize while maintaining the molding temperature without substantially shrinking the entire bottom of the secondary molded product. I have. If the bottom is made thicker in this way, a complicated heating method for the secondary molded article is required, and the basis weight is increased by the thickness of the bottom.
There is also throat problems, it is required to solve such problems.

Accordingly, an object of the present invention is to provide a two-stage process in which a secondary molded product stretched by primary blow molding is heat-shrinked to a more preferable form and subjected to secondary blow molding without employing a complicated heating form. An object of the present invention is to provide a method for producing a biaxially stretched blow molded container by blow molding. Another object of the present invention is to provide a method for producing a biaxially stretched blow-molded container having a particularly strengthened bottom and excellent heat resistance, pressure resistance, and heat pressure resistance.

[0009]

According to the present invention SUMMARY OF], a process for the preparation of biaxially oriented plastic containers by blow molding a preform which has been heated to the stretching temperature, and the primary blow-molded preform, bottom center Part and its immediate vicinity
A step of a biaxially oriented secondary molded article having a domed bottom that is sufficiently stretched, except for while pressing the bottom center with heating the de chromatography arm shaped bottom portion of the secondary molded article, the bottom Shrinking preferentially, a step of forming a tertiary molded product in which the bottom center is depressed and the periphery is flattened, and the tertiary molded product is
Heat the bottom and torso, including the torso, mainly to shrink the torso
Biaxially stretched blow container having a reinforced bottom portion, comprising the steps of : forming a quaternary molded product by heating, and secondary blowing the heated quaternary molded product into a final container shape. Is provided.

[0010]

According to the present invention, in the two-stage blow molding method, the molded product immediately before the secondary blow molding, that is, the molded product which has undergone the heat shrinkage step after the primary blow molding is formed as close as possible to the shape of the desired final product. Thereby, the processing rate by the secondary blow molding is reduced, the thickness of the molded product is made uniform, and a decrease in crystallinity is prevented. Since the bottom of the container requires a large amount of processing due to requirements such as heat resistance, pressure resistance, and self-sustainability, it is a part that becomes a problem even in two-stage blow molding.
In the present invention, in particular, in order to reinforce the bottom portion, the shape of the bottom portion of the molded product (tertiary molded product) immediately before being subjected to the secondary blow molding is to have a shape in which the bottom central portion is depressed and the periphery is flattened. , Is an important feature.

In order to make the bottom shape of the tertiary molded product into a shape in which the bottom center portion is depressed and the periphery is flattened, first, a biaxially stretched secondary molded product having a dome-shaped bottom portion is formed in primary blow molding. . Next, before the secondary molded article is subjected to secondary blowing, the entire bottom is heated to a shrinkage temperature or higher and shrunk while pressing the center of the bottom. The center can be easily dented, and the periphery can be contracted with a flattened bottom shape with almost no change in diameter.

The dome-shaped bottom is flattened so as to reduce its surface area by being heated to the shrinkage temperature or higher. At this time, by mechanically pressing the center of the bottom, the center can be easily deformed without affecting the flattening of the bottom. In this case, the deformation due to the pressing of the bottom center part proceeds with the shrinkage and softening of the bottom part due to the heating, and it is usually possible to perform the concave part of the bottom part and the flattening process of the periphery without substantially stretching. it can. For this reason, it is possible to work in a concave shape with a relatively small pressing force, and it is possible to work only the bottom part without exerting the influence of the working on the body part of the molded product. Tertiary molded products having such a bottom shape are:
The processing rate by secondary blow molding can be reduced,
As a result, it is possible to ensure a preferable bottom wall thickness distribution and effectively prevent a decrease in crystallinity and the like.

In the present invention, the dome-shaped bottom portion of the secondary molded product contracts substantially in a flat plate shape by heating, but the heating causes a large temperature rise in a thin portion,
It tends to shrink at the beginning, and therefore it is desirable that the bottom of the secondary molded article has a relatively uniform thickness distribution except for the center of the pressed bottom. Also, the bottom central portion may include a portion that is substantially unstretched and thicker than its surroundings,
In this case, it is preferable to press the periphery of the central thick portion to form a concave shape. Furthermore, it is preferable that the bottom of the secondary molded product formed by primary blow molding is generally a dome shape that is convex outward, but it may include a concave portion in which the center of the bottom is slightly concave inward. By well pressing the recess, the recess can be smoothly processed.

In the present invention, the stretchable temperature (90 to 110)
The preform heated to (° C) is subjected to primary blow molding by either a free blow molding method in which blow molding is performed without using a mold or a mold blow molding method in which blow molding is performed using a mold. To obtain a secondary molded product.
At that time, except for the unstretched portion at the bottom center and the vicinity of the neck, the thickness of the body and bottom of the secondary molded product is substantially 0.6 mm or less,
By setting the thickness to preferably 0.2 to 0.5 mm, it becomes possible to perform heating in the subsequent shrinkage heating and heat setting steps in a short time. The thickness of the heated part is 0.6mm
If the heating temperature exceeds the above range, the temperature distribution in the thickness direction becomes too large by heating for a short time, and it is difficult to keep the temperature within a preferable temperature range.

When a secondary molded article is manufactured from a preform by primary blow molding, an axial stretching ratio is 2 to 5 times,
In particular, 2.2 to 4 times, the stretching ratio in the circumferential direction is 2.5 to 6.
The stretching ratio is preferably 6 times, especially 3 to 6 times. In the free blow molding method, the stretching ratio in the axial direction and the circumferential direction is determined according to the shape and the heating temperature of the preform molded product and the blow molding conditions such as the blow molding pressure or the form of stretching with a stretching rod.

Next, the secondary molded article is subjected to a heat setting step, and firstly, the bottom is heated preferentially and pressed to form a tertiary molded article having a concave bottom center.
Next, the bottom and the trunk are heated, and the trunk is thermally shrunk mainly in the height and radial directions to form a quaternary molded product. As the heating means, various means such as a heating method using hot air or a solid contact heating method in which a flat heating element is sequentially pressed from the dome-shaped top and heated can be used, but in the present invention, an infrared heating method is used. It is particularly preferred to employ In the infrared heating method, compared with heating by heat conduction from the surface using hot air, a part of infrared rays is transmitted and absorbed to the inside of the plastic, so that heating can be performed relatively efficiently. In addition, the desired heating can be performed in a relatively short time of about 1 to 15 seconds by allowing the secondary molded article to pass through the tunnel-shaped heating body combined with the planar infrared radiator while rotating. Can be. The temperature at which the secondary molded product starts shrinking by heating depends on the stretching conditions of the primary blow molding, the temperature at the time when the internal pressure of the secondary molded product molded by the primary blow molding is released, and the like, and is usually 60 to 140 ° C. Start shrinking by about a degree. The molding temperature at which blow molding can be performed in the secondary blow molding is usually 90 to 110 ° C. or higher, and the secondary molded product is heated to a shrinkage temperature and a stretching temperature or higher. In the case of a heat-resistant container, the body and bottom of the secondary molded product are finally adjusted to 130 to 22.
It is preferable to heat to a temperature of about 0 ° C. and go through a heat setting step of sufficiently thermally crystallization.

The quaternary molded article is finished heating with shrinkage of the container is being performed, is crystallized, residual stress is relaxed. In addition, it is cooled somewhat before being subjected to the secondary blow molding step, and the temperature difference between the inner and outer surfaces is reduced by the heat conduction effect in the thickness direction. Usually, a relaxation time of about 0.3 to 3 seconds is provided. In the secondary blow molding step, the mouth and neck are restrained, and the heated quaternary molded product is stretch blow-molded using a mold having a bottom and a body. Such secondary blow molding is preferably performed using a gas of 15 to 40 kg / cm ² . Further, in a container that requires heat resistance, it is preferable that the mold temperature is maintained at a temperature of about 70 to 130 ° C. to prevent rapid cooling of the molded product during the secondary blow molding.

In the present invention, plastics include
Any plastic can be used as long as it can be stretch blow-molded and heat-fixable, but a thermoplastic polyester, particularly an ethylene terephthalate-based thermoplastic polyester, is advantageously used. Of course, polycarbonate, arylate resin and the like can also be used. As the ethylene terephthalate-based thermoplastic polyester, ethylene terephthalate units occupy most of ester repeating units, generally 70 mol% or more, particularly 80 mol% or more,
A glass transition point (Tg) of 50 to 90 ° C., especially 55 to 80 ° C., and a melting point (Tm) of 200 to 275 ° C., especially 2
Thermoplastic polyesters between 20 and 270 ° C. are preferred. Homopolyethylene terephthalate is preferred in terms of heat resistance, but a copolymerized polyester containing a small amount of ester units other than ethylene terephthalate units can also be used.

Examples of dibasic acids other than terephthalic acid include aromatic dicarboxylic acids such as isophthalic acid, phthalic acid and naphthalenedicarboxylic acid; alicyclic dicarboxylic acids such as cyclohexanedicarboxylic acid; succinic acid, adipic acid, sebacic acid and todecanedione. One or a combination of two or more of aliphatic dicarboxylic acids such as acids; diol components other than ethylene glycol include propylene glycol, 1,4-butanediol, diethylene glycol,
One or more of 1,6-hexylene glycol, cyclohexane dimethanol, an ethylene oxide adduct of bisphenol A and the like can be mentioned.

The ethylene terephthalate-based thermoplastic polyester to be used should have at least a molecular weight sufficient to form a film, and an injection grade or an extrusion grade is used depending on the application. This intrinsic viscosity (IV) is generally from 0.6 to 1.4 dl / g, in particular from 0.
Those in the range of 63 to 1.3 dl / g are preferred.

Injection molding can be used for molding a plastic preform. That is, the plastic is melt-injected into a cooled injection mold, cooled,
Mold into an amorphous plastic preform. As the injection machine, a known injection machine having an injection plunger or a screw is used, and the mixture is injected into an injection mold through a nozzle, a sprue, and a gate. As a result, the polyester or the like flows into the injection mold cavity and is solidified to form a preform for stretch blow molding. As the injection mold, one having a cavity corresponding to the shape of the container is used, but it is preferable to use a one-gate or multi-gate injector. Injection temperature is 270 to 310
The temperature and the pressure are preferably about 28 to 110 kg / cm ² .

[0022]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to the accompanying drawings. FIG. 1 shows an example of a process for producing a heat-resistant container according to the present invention. In FIG. 1, a preform molded article 1 (FIG. 1 (A)) molded by injection molding or the like is heated to a temperature at which stretching is possible (90 to 110 ° C.), biaxially stretch blow-molded, and a dome-shaped bottom is formed. Secondary molded product 2 having a shape
(FIG. 1B) is obtained. Next, in FIG. 1 (C) showing a step of heating and shrinking while pressing the bottom of the secondary molded product, a heating body 3 and a vertically movable pressing rod 4 are arranged at portions corresponding to the bottom. In this step, the bottom of the secondary molded article 2 is heated by the heating element 3 to a temperature equal to or higher than the shrinkage temperature to shrink, and the pressing rod 4 descends from above and presses the center of the bottom to form a dent. At this time, it is preferable that the pressing rod is configured such that the dome-shaped bottom of the secondary molded product is contracted into a flat plate shape by heating and descends according to the descending speed,
It is preferable that the pressing rod is pressed by its own weight or a relatively small force of about several kgf or less, and the lowering of the pressing rod is stopped when a predetermined depression is obtained. Thereby, when pressing the bottom of the secondary molded product, the concave processing is performed with substantially no stretching. The hemispherical bottom of the secondary molded product is depressed inward at the center by pressing with a pressing rod, and is sufficiently stretched at the time of primary blow molding except for the center of the bottom and its immediate vicinity. The tertiary molded product 5 having a bottom shape as shown in FIG. 1 (D) is formed by shrinking in a flat plate shape so as to reduce the surface area. The diameter of the bottom of the tertiary molded product is almost the same as that of the secondary molded product. Further, it is preferable that the bottom is heated from the top at the center of the bottom to start shrinkage, and the heat shrinkage is sequentially expanded in the radial direction.

The temperature at which shrinkage due to heating of the secondary molded product is started is determined by the blow molding conditions of the secondary molded product, particularly by performing blow molding.
Since it depends on the temperature at the time when the secondary molded article shrinks by releasing the blow pressure, shrinkage by heating usually starts in a temperature range exceeding the temperature. The mold temperature in the mold blow molding method, the contact state and the time of the mold and the secondary molded article, or the degree or the like of cooling by blowing air, shrinkage of the secondary molded article
Temperature is affected. The bottom is heated by a heating method using an infrared heater 3 as shown in FIG. The degree of the depression at the center of the bottom formed can be adjusted by the amount of volume change of the flat portion formed by the heat shrinkage of the bottom and the degree of pushing of the pressing rod. Also, the outer diameter of the flattened bottom is adjusted slightly by adjusting the heating area and the degree of heating so that the bottom outer diameter is slightly smaller than the bottom diameter of the secondary blow mold so that it fits in the secondary blow mold. Is preferable.

The body and bottom of the tertiary molded product 5 obtained as described above, the center of which is recessed at the bottom and the periphery thereof is flattened, are further subjected to infrared heating elements 3 and 6 as shown in FIG. To obtain a quaternary molded article 7 whose body and bottom are heated to a preferable crystallization temperature. At this time, the pressing rod 4 has already moved upward. Since the tertiary molded product 5 is heated while substantially maintaining the shape of the contracted bottom portion, the quaternary molded product 7 substantially includes the bottom portion and a part of the trunk portion near the bottom portion as shown in FIG. Except for the other body, the other body has a shape that is contracted in the height and radial directions. The quaternary molded product 7 needs to have a shape slightly smaller than the secondary blow mold.

[0025] Quaternary molded article 7 heated to crystallization temperature
Is blow-molded in a secondary blow mold 8 in a secondary blow molding step shown in FIG. 2A, and is taken out as a final molded article 9 as shown in FIG. 2B. Through the above steps, it is easy to bring the shape of the quaternary molded product close to the shape of the secondary blow molding die, thereby suppressing the processing rate of the bottom corner portion during the secondary blow molding to be low. It becomes possible. As a result, a final molded product excellent in strength and heat resistance can be obtained. Further, the secondary molded product has a generally outwardly convex dome shape. In the primary blow molding, the bottom portion can be molded to a relatively uniform thickness except for the central thick portion and its vicinity, and it is shrunk. In the tertiary and quaternary molded products, and also in the final product, the thickness of the bottom can be made relatively uniform. As a result, a blow container having a relatively thin-walled bottom having excellent strength and heat resistance is obtained,
As a result, the effect that the weight per unit area can be reduced can be exhibited.

In the case of a heat-resistant container, the temperature of about 130 to 220 ° C. is usually maintained in the quaternary molded product immediately before the secondary blow molding to promote thermal crystallization. Heat resistance can be imparted. In particular, by performing stretching / heat shrinkage on the entire bottom, the strength is improved. Further, since the bottom is subjected to a thermal crystallization step, it is possible to impart preferable strength and high heat resistance to the bottom.
Along with this, it is possible to achieve a reduction in the basis weight by reducing the thickness of the bottom.

FIG. 3 shows an example of a method of pressing and pressing the center of the bottom of the secondary molded product in the present invention. FIG.
As shown in (A), the bottom part 10 of the secondary molded product has a dome-shaped bottom part 11 that is sufficiently stretched and a thick part 12 whose central part is unstretched. The pressing rod 13 that can move up and down so as to press the bottom center has a concave shape such that its tip surrounds the unstretched thick part 12 at the bottom center.
2. Press around 2. At the same time as being heated by the heating body (not shown), the bottom portion 10 of the secondary molded product is mechanically pressed by a pressing rod, and becomes a tertiary molded product 14 having a bottom shape shown in FIG. The tertiary molded product 14 includes the thick portion 12
, The center of the bottom is indented inwardly of the container, and the periphery thereof is a flat bottom.

FIG. 4 is a view showing one embodiment of an apparatus for producing a biaxially stretched blow container by the method of the present invention,
In the primary blow molding step indicated by reference numeral 15 as a whole, the preform 16 is supplied to the primary blow mold 17 to perform blow molding. Next, the secondary molded product 18 passes between a pair of infrared heating bodies 19a and 19b opposed to the body and a tunnel-shaped heating device 19 including a planar infrared heating body corresponding to the bottom not shown. (Bottom processing step 2
0). Although not shown, a pressing rod corresponding to the center of the bottom is arranged in this heating device. As a result, the bottom of the secondary molded product 18 is dented at the center and the periphery thereof is contracted in a flat plate shape, and then the trunk is contracted in the height direction and the radial direction, and finally heated to the crystallization temperature (heat setting). Step 21) becomes a quaternary molded product 22. Next, the quaternary molded product 22 is supplied to a secondary blow mold 24 in a secondary blow molding step indicated by 23, is subjected to secondary blow molding, and is taken out as a final molded product 25.

In this apparatus, the first bottom heating (FIGS. 1C and 1D) and the second body and bottom heating (FIG. 1E) have cross sections as shown in FIG. This is performed by the secondary molded article 18 traveling while rotating in an infrared heating device 19 arranged on the circumference in a tunnel shape similar to E). Each infrared heating element constituting the infrared heating device 19 is divided into several parts on the circumference and the temperature can be adjusted, and the temperature rise at the bottom of the secondary molded product is more than the temperature rise at the body. Is also controlled to be large. As a result, first, the center of the bottom is dented and the periphery thereof contracts in a flat plate shape, second, the trunk is contracted, and finally the trunk and the bottom have a predetermined crystallization temperature.

In the method of the present invention, various changes can be made to the above basic steps. For example, as shown in FIG. 5, by performing primary blow molding using a mold having a hemispherical bottom and a slightly concave center, a secondary molded article 33 is formed along the mold. (FIG. 4
(A)). Next, the central portion of the secondary molded product 33 is pressed with a pressing rod, and the bottom and a part of the body connected to the bottom are heat-shrinked. It is created (FIG. 5B). Further, the tertiary molded product 34 can be subjected to secondary blow molding to obtain a final product 35 having a relatively deep concave bottom shown in FIG. 5D (FIG. 5C). In this case, only the bottom part and its vicinity of the secondary molded article 33 subjected to the primary blow molding shrinks by heating, and is deformed by the secondary blow molding, and the other body becomes the final product 35 without being heat shrunk. Therefore, it is suitable for a pressure-resistant or heat-resistant container having no unevenness such as a panel on its body. In FIG. 5A, the shape of the bottom of the secondary molded product is a hemisphere having a relatively small radius of curvature, and a relatively large surface area for heat shrinkage is obtained. A sufficient area for forming a tertiary molded product having a concave bottom is secured, and a minute recess is provided in the center of the secondary molded product, so that the pressing by the pressing rod can be performed smoothly. . As a result, a final product having a relatively deep concave, relatively uniform and thick bottom can be finally formed, and such a bottom has excellent pressure resistance or heat pressure resistance. In addition, by performing primary blow molding using a primary blow mold whose bottom is at a higher temperature than the trunk, and obtaining a secondary molding at which the bottom is at a higher temperature than the trunk, a secondary molded product is obtained. Flattening due to heat shrinkage of the bottom can be promoted.

Further, in the example shown in FIG. 5, in the heating step of the secondary molded article, the temperature of the secondary molded article can be stretched without substantially shrinking the body portion (85 to 130 ° C.).
Approximately), heat shrinking and concave processing of the bottom part are mainly performed to make a tertiary molded product, and in the next secondary blow molding step, in addition to the stretching of the bottom part, the body part is also slightly stretched and finished. It can be shaped. In this case, by using a relatively high temperature mold in the primary blow molding, the body of the obtained secondary molded product can be stretched to a temperature at which it can be stretched (85 ° C. or higher).
In the next heating step, it is necessary to heat the body so as to maintain the body in a temperature range where it can be stretched and does not substantially shrink.

In a container for heat-resistant pressure, pressure resistance and 70-80 ° C.
It is required to have heat resistance to withstand a certain degree of heat treatment. In the above method, the strength and heat resistance can be sufficiently obtained by performing primary blow molding with a relatively high temperature mold in the body, and by performing secondary blow molding while maintaining that state, In secondary blow molding, only slight stretching is required. As a result, the contraction of the secondary molded product only requires the bottom to be depressed from the dome shape to the central portion and the periphery to be deformed into a flat plate shape, as compared to the case where the body is shrunk in the height and radial directions. It is easy to control the height and diameter of the tertiary molded product inserted into the secondary blow mold, and it is possible to reduce variations in shape due to heating. Therefore, since the shape of the tertiary molded product can be very close to the shape of the secondary blow mold,
In particular, there is an advantage that the processing rate at the time of secondary blow molding of the bottom can be suppressed as small as necessary.

Further, in the heat shrinking of the bottom of the secondary molded article and the pressing of the center of the bottom, a pressing and heating jig comprising a combination of a heated support plate 26 and a pressing rod 27 as shown in FIG. Can also be used. This pressing and heating jig is configured such that the pressing rod 27 is supported on the heating support plate 26 via an elastic member 28 such as a spring so as to be able to move up and down independently, and the entire pressing and heating jig can also move up and down. , Are installed facing the bottom of the secondary molded article 29 (FIG. 6A). As shown in FIG. 6B, the secondary molded product 2
The entire pressing and heating jig moves in the direction of the arrow such that the heating support plate 26 is in contact with the bottom of the heating support 9. Next, only the pressing bar 27 moves downward. As a result, the bottom of the secondary molded article 29 is flattened by the contact heating by the heating support plate 26, and a depression is formed inward at the center of the bottom by pressing by the pressing rod 27, and the center of the bottom is depressed and the periphery thereof is formed. The flattened tertiary molded product 30 is formed (FIG. 6C). Thereafter, the entire pressing and heating jig moves upward, and the bottom and the trunk of the tertiary molded product are heated and shrunk by the tunnel-shaped heating element 31 to form the quaternary molded product 32 (FIG. 6 (D)). )).

(Production Example) Using the apparatus shown in FIG. 4, the final molded product has an outer diameter of 94 mm, a total height of 305 mm (heating section height of 280 mm), a capacity of 1500 ml and a concave bottom.
A polyethylene terephthalate (PET) bottle for heat resistance as shown in (B) was prepared.

Heating a predetermined preform to 100 ° C.
Primary blow molding was performed using a mold kept at 70 ° C. to obtain a secondary molded article having a hemispherical bottom part having a relatively uniform thickness except for a thick part at the center. The secondary molded product is divided into three zones on the circumference, and each part is 500 to 700 ° C.
By passing through a bottom forming device and a heat setting device consisting of a bottom-shaped pressing device with a tunnel-shaped infrared heating body and a pressing rod temperature-controlled in the surface temperature region for 8 seconds while rotating, the first bottom portion is It is deformed so that it is concave at the center and flat at the periphery, second, the body shrinks in height and radial direction, and finally the temperature of the body and bottom is approximately 180 ° C. A molded product was obtained. Further, this quaternary molded product was subjected to secondary blow molding to obtain a final product. This final product was filled with hot water of 95 ° C., and the heat resistance was evaluated from the volume change rate (good range: volume change rate of 2% or less).
Good results were obtained.

[0036]

According to the present invention, a two-stage process in which a secondary molded product stretched by primary blow molding is heat-shrinked to a more preferable shape and subjected to secondary blow molding without employing a complicated heating mode. By the blow molding, a biaxially stretched blow molded container excellent in heat resistance, pressure resistance and heat pressure resistance could be manufactured. Further, the strength in the vicinity of the bottom of the molded container is improved, and it is possible to reduce the weight per unit area because it has a relatively uniform thickness distribution as well as a local thin portion. In addition, a bottom-shaped container having a relatively deep hollow can be created by mechanically pressing the center of the bottom in the bottom processing step of the secondary molded product, and a biaxial stretch blow having an improved strength at the bottom of the container is provided. A molded container could be manufactured.

[Brief description of the drawings]

FIG. 1 is a view for explaining an example of a molding step of the present invention.

FIG. 2 is a view for explaining an example of a molding step of the present invention.

FIG. 3 is a view for explaining a method of pressing the bottom of a secondary molded product according to the present invention.

FIG. 4 is a diagram showing an overall arrangement of an example of a manufacturing apparatus for carrying out the method of the present invention.

FIG. 5 is a view for explaining another example of the molding step of the present invention.

FIG. 6 is a view for explaining a method of pressing the bottom of the secondary molded product according to the present invention.

[Description of sign]

 DESCRIPTION OF SYMBOLS 1 Preform 2 Secondary molding 3, 6 Heating body 4 Pressing rod 5 Tertiary molding 7 Quaternary molding 8 Secondary blow mold 9 Final molding

──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Kimio Takeuchi 2297-5 Nogawa, Miyama-ku, Kawasaki City, Kanagawa Prefecture (72) Inventor Hideo Kurashima 3-26-16 Iwato, Yokosuka City, Kanagawa Prefecture (72) Inventor Yoshitsugu Maruhashi 6-35-5 Hiyoshihoncho, Kohoku-ku, Yokohama-shi, Kanagawa Prefecture (56) References JP-A-6-143392 (JP, A) EP 571262 (EP, A1) (58) Fields investigated (Int. . ^7, DB name) B29C 49/00 - 40/80

Claims (1)

(57) [Claims] 1. A method for producing a biaxially oriented plastic containers by blow molding a preform which has been heated to the stretching temperature, the preform was the primary blow-molded, bottom center portion and its
A step of a biaxially oriented secondary molded article having a domed bottom that is sufficiently stretched except very near the presses the bottom center with heating the de chromatography arm shaped bottom portion of the secondary molded article While the bottom is preferentially shrunk, a step of forming a tertiary molded product having a concave bottom center and a flattened periphery, and heating the tertiary molded product including its bottom and body,
A biaxially reinforced bottom part comprising a step of mainly shrinking the body to form a quaternary molded article, and a step of performing secondary blow molding of the heated quaternary molded article into a final container shape. A method for producing a stretch blow container.