JPH0220413B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a multilayer stretch blow molding bottle, and more particularly to a method for manufacturing a molecularly oriented multilayer plastic bottle by stretch blow molding without the possibility of forming pinholes at the bottom joint. .

The inner and outer layers are made of polyolefin resin, and the middle layer is made of ethylene-vinyl alcohol copolymer or polyamide resin (if necessary, an adhesive layer made of, for example, carboxyl group-modified polyolefin resin is interposed between the inner layer and the middle layer and between the outer layer and the middle layer). Containers formed from laminates made of a combination of resins with excellent moisture permeability and resins with high oxygen permeability, such as laminates made of By forming such a container by a stretch blow molding method and molecularly orienting the resin, container properties such as transparency, strength, impact resistance, and gas barrier properties can be further improved.

As a manufacturing method for such a multilayer stretch blow-molded container, for example, as disclosed in JP-A-49-32962, a multilayer melt-extruded tubular body mainly made of polypropylene is rapidly cooled and then cut into a predetermined length. There is a known method in which this is then stretched and oriented in the tube axis direction at a molecular orientation temperature (a temperature between the crystalline melting temperature and the thermal melting point of polypropylene), and then blow molded in a mold. In this method, the bottom of the container is formed by pressing one end of a tubular body stretched in the tube axis direction at a molecular orientation temperature between opposing surfaces 1a of the bottom of the half-split mold 1 (Fig. 1). A protruding joint 2 is formed at the bottom.
In this case, a pinhole may be formed in the joint 2, and the liquid content may leak. The reason for this is not necessarily clear, but it is estimated as follows: (1) Since the bonding is performed below the melting point, the bonding surface 2a
are not completely integrated. (2) Since the deformation strength of the inner layer 3a, the outer layer 3b (e.g. polypropylene layer) and the intermediate layer 3c (e.g. ethylene-vinyl alcohol copolymer) at the stretching temperature is different, especially when the deformation strength of the intermediate layer 3c is higher, , inner layer 3a
The deformation of the intermediate layer 3c cannot follow the deformation of the intermediate layer 3c, resulting in a crack (pinhole) extending in the direction of arrow 4.
Furthermore, the interface at the joint 2 between the inner layer 3a and the intermediate layer 3c is also caused by slips, etc. (the inner layer 3a and the intermediate layer 3c
Pinholes are likely to occur even if an adhesive layer (not shown) (made of carboxyl group-modified polypropylene, for example) is interposed between c. Therefore, pinholes can easily penetrate along the directions of arrows 4 and 5.

Furthermore, in the case of the above manufacturing method, (1) the shape of the thread at the neck part is difficult to accurately form due to the low molding temperature, (2) the gas barrier properties at the joint part 2 are poor (as shown in Fig. 3, the intermediate layer 3c (for example, (3) Due to the structure of the mold, the pressure resistance required for carbonated beverage containers, etc. (4) Since the outer diameter of the tubular body is regulated by the thread diameter of the neck, the tubular body must be thick. Therefore, there are problems such as it takes time to heat up to the stretching temperature and the temperature difference in the wall cross section tends to become large.

The present invention aims to solve the problems of the prior art as described above.

The method for manufacturing a multilayer stretched blow bottle of the present invention includes melting and extruding a multilayer plastic tubular body using a multilayer extrusion die, and extruding the multilayer plastic tubular body in a molten state. The upper and lower ends of the part are closed by a pair of cooled half molds, which have a circumferential groove on the inner surface upper part of the shape corresponding to the threaded part, and the part of the tubular body is immediately closed. A hollow needle is inserted into a portion above the level of the circumferential groove, and pressurized gas is blown into the closed tubular body portion through the hollow needle to bring the tubular body portion into close contact with the inner surface of the mold. Please,
The tubular body is rapidly cooled to a temperature below the crystallization start temperature of the plastic layer mainly constituting the tubular body, and then the mold is opened and the tubular body portion is cut at the upper end of the neck portion to form a bottomed body having the neck portion. After forming a parison and uniformly heating the bottomed parison except for the neck portion to a temperature at which stretch molding is possible, the bottomed parison is charged into a stretch blow molding mold, and the neck portion is fixed. It is characterized in that pressurized gas is blown into the bottomed parison at the same time as or slightly after the stretching in the axial direction.

Furthermore, in addition to the above manufacturing method, the present invention provides the following features: (1) The upper and lower ends of a portion of the tubular body in a molten state are provided with a hanging portion on a pair of inner surfaces and a tapered portion connected to the hanging portion and extending inwardly and downwardly. or (2) bringing the tubular body portion into close contact with the inner surface of the mold, and approximately at the same time as the close contact, the level of the circumferential groove of the tubular body portion is closed. Provided is a method for producing a multilayer stretched blow bottle, characterized in that a second hollow needle is inserted into the upper part and cold water is fed into the tubular body part through the second hollow needle. It is.

The present invention will be described below with reference to drawings for explaining embodiments.

In FIG. 2, reference numeral 6 denotes a multilayer extrusion die, from which a multilayer plastic tubular body 7 (hereinafter referred to as tubular body) is melt-extruded from a nozzle (not shown). The structure of the tubular body 7 is as shown in FIG. 3, in which the inner layer 7a and the outer layer 7b are made of polypropylene (herein, crystalline homopolypropylene or a crystalline copolymer mainly composed of propylene, and crystals mainly composed of the above). The intermediate layer 7c is made of an ethylene-vinyl alcohol copolymer (for example, vinyl alcohol content is about 40 to 80 mol%), and the inner layer 7a and the intermediate layer 7
A five-layer structure in which an adhesive layer 7d of carboxyl group-grafted polypropylene is interposed between the outer layer 7b and the intermediate layer 7c and between the outer layer 7b and the intermediate layer 7c (the thickness ratio is, for example, inner layer 7a, outer layer 7b:intermediate layer 7c:adhesion). agent layer 7d
= 100:2:4), but the present invention is not limited to the above configuration; for example, the intermediate layer 7
c may be a polyamide resin (for example, a copolymer of nylon 6 and nylon 66). Moreover, the inner layer 7a and the outer layer 7b may be made of polyolefin resin other than polypropylene. Furthermore, the inner layer and outer layer are made of carboxyl group-modified polyolefin resin (for example, carboxyl group-modified polypropylene),
The intermediate layer may have a three-layer structure made of ethylene-vinyl alcohol copolymer or polyamide resin.

A mold 8 for forming a parison is provided directly below the nozzle of the extrusion die 6, and is composed of a pair of half-split molds 8a facing each other. The half-split mold 8a has protrusions 9 and 10 at the top and bottom, respectively, and a cavity 11 with a slightly larger inner diameter is provided in the middle by the tubular body 7 (the opposing upper protrusion 9 and lower protrusion 10 allow the tubular body 7 to (in a state in which the upper and lower ends of a predetermined portion 7' including a portion to become a parison are pressed and fused). A circumferential groove 12 having a shape corresponding to the threaded portion of the parison is formed in the upper part of the inner surface of the half-split mold 8a. In addition, cooling holes 13 are provided in the half-split mold 8a, and the inside of the mold is, for example, 5 to 5.
Cooling water at 10℃ flows through it.

As shown in FIG. 3, the inner surface of the lower protrusion 10 includes a hanging portion 14 (preferably about 3 to 4 mm in height) extending perpendicular to the plane of the paper, and a tapered portion 15 extending inwardly downward and connected to the lower part. (The angle between the opposing tapered portions is preferably about 60 to 90 degrees). By doing this,
As shown in FIG. 3, the intermediate layers 7c on both sides of the tubular body 7 are joined at the lower end, and the lower part of the joint 16 is closed by the intermediate layer 7c.
This is because a gas barrier is ensured.

A through hole 17 is provided slightly above the circumferential groove 12 of one half mold 8a, and a hollow needle 18 is slidably inserted through the through hole 17. Reference numeral 19 denotes an air cylinder for sliding the hollow needle 18 along the through hole 17. When pressurized air is supplied from the conduit 20, the hollow needle 18 advances to the left in the figure and slides through the tubular body. A hole is made in the wall of a predetermined portion 7' (hereinafter referred to as the tubular body portion), and its tip 18a penetrates into the interior of the tubular body portion 7' as shown in FIG. When supplied, the tip 18a is configured to return to its original position as shown in FIG. 22 is a pressurized air source for sending pressurized air for parison blow molding into the hollow needle 18;
3 is a direction switching solenoid valve. A second through hole 24 and a through hole 2 are formed slightly above the circumferential groove 12 of the half mold 8a.
A second hollow needle 25 is provided which is slidably inserted through the hole 24, and the hollow needle 25 is reciprocated within the through hole 24 by an air cylinder (not shown) having the same configuration as the air cylinder 19. The hollow needle 25 communicates with a cooling water source (not shown) via a solenoid valve (not shown). The reciprocating movement of the hollow needles 18 and 25 and the switching of the solenoid valve 23 are configured to be performed at timings described later by a control mechanism (not shown).

With the above device, the bottomed parison 26 (fifth
6) is formed in the following manner. The upper and lower ends of the molten tubular body portion 7' are closed by the mold 8 as shown in FIG. 2, a joint 16 is formed at the bottom, and the hollow needle 18 is immediately inserted into the second
As soon as the tip 18a enters the tubular body portion 7', the solenoid valve 23 is switched to blow pressurized air into the tubular body portion 7', and the tubular body 7' is moved to the left as shown in FIG. The part 7' is the inner wall of the cavity 11,
That is, the parison blank 2 is cooled by being brought into close contact with the inner surface of the mold 8, and at the same time the threaded portion 27 is formed.
6' is formed. From the viewpoint of stretchability and transparency, it is necessary that the parison blank 26' not develop large spherulites. Therefore, the above-mentioned cooling is performed at least to the crystallization initiation temperature (usually about 100 to 120°C) of the plastic layer mainly constituting the parison blank 26', for example, polypropylene in the above example.
It is necessary to carry out the process in such a way that it is rapidly cooled to below. If the parison blank 26' has a thick wall and the inner surface of the parison blank 26' is not sufficiently rapidly cooled by cooling only the outer surface, cold water may be introduced into the parison blank 26'. That is, as soon as the parison blank 26' is formed by the above-mentioned close contact, the hollow needle 25 is inserted into the parison blank 2.
At the same time, cold water is introduced into the parison blank 26' through the hollow needle 25 (for example, by spraying it in the form of a mist), and at the same time, the solenoid valve 23 is switched. The interior of the balisong blank 26' is rapidly cooled by the cold water, and the air inside and the generated water vapor are discharged into the atmosphere from the discharge port 23a of the electromagnetic valve 23 through the hollow needle 18. Next, hollow needles 18 and 2
5 is returned to its original position, and then the mold 8 is opened. After that or at an appropriate time, the cutter 28 cuts the lower end of the unformed portion of the tubular body 7.
Next, the parison blank 26' is cut in the diametrical direction at a predetermined position between the upper part of the threaded part 27 of the parison blank 26' and the perforated part by the hollow needle 18, to obtain a bottomed parison 26 having a neck part 29 and a bottom part 30. Form. After performing mechanical finishing to remove burrs and the like as necessary, the bottomed parison 26 is biaxially stretched and blow molded by a method as exemplified below. Note that the shape of the cavity 11 of the mold 8 may be determined so that the diameters of the body portion 31 and bottom portion 30 of the bottomed parison 26 are slightly larger than those of the neck portion 29. By doing this, the stretching ratio in the circumferential direction becomes slightly smaller, but the wall thickness of the parison body becomes thinner, so rapid cooling becomes easier, and the heating time for stretch blow molding is shortened, so it is possible to This makes it easier to prevent the formation of spherulites.

In FIG. 7, 32 is a body mold of a stretch blow molding mold, 33 is a neck part, and 34 is a bottom mold, each of which has an inner surface maintained at a predetermined temperature by a liquid flowing through a conduit hole (not shown). There is. Reference numeral 35 denotes an elongated rod, into which a guide hole 35a for guiding the blown gas is provided. The bottomed parison 26 has a neck part 29
After being heated uniformly by infrared heating etc. while preferably being rotated to a temperature that allows stretching and forming,
The neck part 29 is held between the neck mold 33 and the body mold 3
2 and a bottom mold 34. The temperature at which stretch-forming is possible is controlled by the melting point or softening point of the plastic in each layer constituting the bottomed parison 26, so its range is very narrow. For example, if the inner and outer layers are polypropylene and the middle layer is ethylene-vinyl alcohol, In the case of a polymer, the range is extremely narrow, such as 156 to 161°C (this temperature varies depending on the vinyl alcohol content of the copolymer). This is because if the temperature is higher than the above upper limit, the ethylene-vinyl alcohol layer will flow during molding, whereas if it is lower, the layer will not stretch and will be cut.

The bottomed parison 26, whose body part 31 and bottom part 30 are uniformly heated to the above-described stretching temperature and which is charged into the cavity 36, is immediately moved to the drawing rod 35.
The joint 16 is stretched in the axial direction of the tube until it comes into contact with the inner surface of the bottom mold 34, and is blown in by pressurized gas (for example, air) introduced through the guide hole 35a at the same time or with a slight delay. The multi-layer stretch blow molded bottle 3 is molded as shown in FIG.
7 is formed. The joint 16 is then folded in as shown in FIG. Next, Netsuku type 33
Then, the barrel mold 32 is opened and the bottle 37 is taken out from the mold. In the above example, the bottom 37a of the bottle 37
Although it has a hemispherical shape, depending on the application, it may have a peripheral annular protrusion, and the inner side of the protrusion may be a substantially flat bottom part that provides erecting stability. Further, the biaxial stretch blow molding method and the mold used therein are not limited to the above examples, and any known means may be employed.

According to the present invention, since the joint at the bottom of the parison is formed at a temperature higher than the melting point, the inner layers are completely thermally fused to each other, and no cracks occur in the inner layer during the formation, so there is no pinhole in the joint. This has the advantage that there is no risk of this occurring. Similarly, it is easy to obtain an accurate shape for the threaded portion.
Furthermore, by forming a tapered part on the inner surface of the lower protruding part of the parison forming mold and extending inwardly and downwardly in connection with the hanging part, the above-mentioned joint part can be made into an intermediate layer with high gas (e.g. oxygen) barrier properties. It is possible to completely occlude the layer, thereby ensuring a high gas barrier property of the bottle. Furthermore, it has the advantage that the parison can be easily quenched by bringing it into close contact with a cooled mold during parison molding, and by feeding cold water into the interior almost simultaneously with the close contact. Furthermore, since a bottomed parison is stretch-blow molded, it is possible to manufacture a bottle having a bottom of any shape. Furthermore, since the cavity shape of the parison-forming mold can be freely selected, it is also possible to form a bottomed parison with a body section that has a larger diameter than the neck section, and therefore the wall thickness of the body section can be reduced. By making it relatively thin, it is also possible to shorten the heating time to the drawing temperature (which contributes to preventing whitening due to the development of spherulites) and to reduce the temperature difference in the wall cross section.
Furthermore, appropriate selection of layer materials constituting the parison;
For example, by using polypropylene for the inner and outer layers and ethylene-vinyl alcohol copolymer for the middle layer, it has excellent water vapor permeability and oxygen permeability, as well as transparency and strength.
It has the advantage that it is possible to produce a stretched blown bottle having excellent container properties such as no heat shrinkage deformation at temperatures (°C).

[Brief explanation of drawings]

FIG. 1 is a longitudinal cross-sectional view of the bottom joint of a multilayer stretched blown bottle produced by a conventional molding method, and FIG. 2 is a longitudinal cross-sectional view of an example of an apparatus including a mold for forming a bottomed parison by the method of the present invention. FIG. 3 is a longitudinal cross-sectional view of the bottom joint formed by the apparatus of FIG. 2; Fig. 4 is a longitudinal cross-sectional view showing a bottomed parison blank formed by the apparatus shown in Fig. 2, and Fig. 5 is a longitudinal cross-section of an example of a bottomed parison blank formed by the apparatus shown in Fig. 2. Fig. 6 is a side view of the bottomed parison shown in Fig. 5 viewed from a direction perpendicular to Fig. 5, and Fig. 7 shows the bottomed parison shown in Fig. 5 inserted into a biaxial stretch blow molding mold. FIG. 8 is a vertical cross-sectional view showing an example of the state after the stretch blow molding of the bottomed parison of FIG. 7 has been completed. 6...Multilayer extrusion die, 7...Multilayer plastic tubular body, 7'... Tubular body part (one part of the tubular body),
8a...Half mold, 12...Peripheral groove, 18...(first)
Hollow needle, 25...(second) hollow needle, 26...bottomed parison, 27...screw part, 29...net part, 32...
Body type, 33...Net type, 34...Bottom type, 37...Multilayer stretched blown bottle.

Claims (1)

[Claims] 1. In a method for manufacturing a multilayer stretched blow bottle having a neck portion having a threaded portion, a multilayer plastic tubular body is melt-extruded using a multilayer extrusion die, and the upper and lower ends of a portion of the molten tubular body are , having a circumferential groove on the upper inner surface with a shape corresponding to the threaded portion;
and closed by a pair of cooled half molds,
immediately inserting a hollow needle into a portion of the closed tubular body section above the level of the circumferential groove and blowing pressurized gas through the hollow needle into the closed tubular body section; The tubular body portion is brought into close contact with the inner surface of the mold and rapidly cooled to below the crystallization starting temperature of the plastic layer mainly constituting the tubular body, and then the mold is opened and the tubular body is placed at the upper end of the neck portion. The portion is cut to form a bottomed parison having the neck portion, and the bottomed parison is heated uniformly to a temperature that allows stretch molding except for the neck portion, and then the bottomed parison is placed in a stretch blow molding mold. A method for producing a multilayer stretched blown bottle, which comprises charging the bottle into a mold, and blowing pressurized gas into the bottomed parison at the same time as stretching in the axial direction with the neck portion fixed, or after a slight delay. . 2. In a method for manufacturing a multilayer stretched blow bottle with a neck portion having a threaded portion, a multilayered plastic tubular body is melt-extruded using a multilayer extrusion die, and the upper and lower ends of a portion of the molten tubular body are aligned with the threaded portion. It has a circumferential groove shaped like this on the upper inner surface,
The inner surface is provided with a lower protrusion having a hanging part and a tapered part connected to the hanging part and extending inward and downward. A hollow needle is inserted into a portion of the tubular body section above the level of the circumferential groove, and pressurized gas is blown into the closed tubular body section through the hollow needle to close the tubular body section. The material is brought into close contact with the inner surface of the mold and rapidly cooled to below the crystallization starting temperature of the plastic layer mainly constituting the tubular body, and then the mold is opened and the tubular body portion is cut at the upper end of the neck portion. After forming a bottomed parison having the neck portion and uniformly heating the bottomed parison except for the neck portion to a temperature at which stretch molding is possible, the bottomed parison is charged into a stretch blow molding mold. A method for producing a multilayer stretched blow bottle, characterized in that pressurized gas is blown into the bottomed parison at the same time as or slightly after stretching in the axial direction while the neck portion is fixed. 3. The length of the hanging portion is about 3 to 4 mm, and the tapered portion is inclined with respect to the hanging portion so that the angle between the opposing tapered portions is about 60 to 90 degrees. A method for producing a multilayer stretched blow bottle as described in Section 1. 4. In a method for manufacturing a multilayer stretched blow bottle having a neck portion having a threaded portion, a multilayer plastic tubular body is melt-extruded using a multilayer extrusion die, and the upper and lower ends of a portion of the molten tubular body are aligned with the threaded portion. It has a circumferential groove shaped like this on the upper inner surface,
and closed by a pair of cooled half molds,
A first hollow needle is immediately inserted into a portion of the closed tubular body section above the level of the circumferential groove, and pressurized gas is passed through the first hollow needle into the closed tubular body section. The tubular body portion is brought into close contact with the inner surface of the mold by blowing into the mold, and almost simultaneously with the close contact, a second hollow needle is inserted into a portion of the tubular body portion above the level of the circumferential groove to form a second hollow Cold water is introduced into the tubular body section through a needle to rapidly cool it below the crystallization temperature of the plastic in the layers that mainly make up the tubular body, after which the mold is opened and the neck section is cooled down. The tubular body portion is cut at the upper end to form a bottomed parison having the neck portion, and after uniformly heating the bottomed parison except for the neck portion to a temperature at which stretch molding is possible, the bottomed parison is is charged into a stretch blow molding mold, and pressurized gas is blown into the bottomed parison at the same time as stretching in the axial direction with the neck portion fixed, or after a slight delay. How to make a blow bottle.