DE2926044C2 - Method and apparatus for manufacturing a container from polyethylene terephthalate - Google Patents

Description

The invention relates to a method for manufacturing a tubular body, a Floor, a standing ring arranged between the body and the floor, and a neck section having container made of polyethylene terephthalate, in which a preform made of amorphous polyethylene terephthalate Axially stretched in a blow mold at the orientation temperature and under the pressure by means of compressed air biaxially orienting the polyethylene terephthalate to the container and then blow molding the the container under internal pressure to intensify the expansion-induced crystallization a temperature higher than the orientation temperature is heated.

In such a known method (US Pat. No. 39,641), after blow molding, the finished molding is cooled by exchanging the blown air for liquid with which the finished container is to be filled. This has the advantage that the container can be cooled down relatively quickly and removed from the mold and the filling process has already taken place. However, there is a risk that especially the mouth and the base area of the container become brittle and milky during the heat treatment, so that the quality of the container is impaired
The invention is therefore based on the object of specifying a method for producing a container from polyethylene terephthalate, in which the occurrence of brittle and / or opaque material areas in the mouth and stand area is avoided.

This object is achieved according to the invention that during the heating the insignificantly oriented portions of the stretching and blow molding Container, including the neck portion, are cooled.

In the invention it was recognized that the heat treatment the non-biaxially oriented sections lead to the formation of so-called spherical crystals, which make the material of the bottle brittle and milky. By cooling these areas during the Heat treatment completely suppresses the formation of spherical crystals while maintaining a amorphous structure of the cooled areas. Only in A certain expansion-related crystallization takes place in the standing area as there is also one in the floor area Some stretching takes place during blow molding. However, the induction of stretch-related crystals leads not to further crystallization as in the rest of the stretched area of the container, because during the heat treatment also the bottom area of a cooling

jo is subject

A device for carrying out the method according to the invention is based on a split blow mold whose cavity corresponds to the dimensions of the container and whose mold halves fluid channel

J5 have ducts. For such a device proposed according to the invention that each of the mold halves corresponding to the container sections in the axial direction viewed is divided into four sections, each thermally insulated from one another by means of an insulating layer.

According to a further embodiment of the invention, each of the insulating layers consists of glass ceramic. With With the aid of such a device, the method according to the invention can be carried out in a simple manner, d. H. the cooling of the stand and muzzle area.

«5 The subject matter of the invention is explained below with reference to the drawing of two embodiments explained. Show it

F i g. 1 to 3 show a longitudinal section of a blow mold during the stretching and inflation of a preform into one

3n container,

F i g. 4 shows a longitudinal section of the blow mold according to FIG. 3 in larger view when removing the container,

F i g. 5 is a plan view of a schematically illustrated system for producing a container according to FIG the second embodiment and

6 shows a side view of a pair of mold halves of the system according to FIG. 5 from the line Vl-Vl in a larger representation.
Embodiment according to FIGS. 1 to 4:

bo In this embodiment, an expanded reservoir 25 wärmebehandeit in the embodiment shown in Figure 4 the blow mold. The two mold halves 16 of which have four sections 16/4 to 16O which are thermally insulated from one another and which are each provided with an insulating layer 13/4. 13S or

ö5 13C made of glass ceramic are separated from one another. Fluid channels 14/4-14D are arranged in the mold halves 16 for thermal conditioning.
The sections 16/4 are used to form a

Neck portion that engages the open portion of a preform 10

The sections t6B together delimit the mold cavity section which forms the tubular body of the container 25 to be manufactured. The sections 16C serve to form the bottom together with the sections 16D. Coolant is supplied to the fluid channels 14Λ in order to reduce the temperature at the neck portion. The fluid channels 14 /? and 14C, heated fluid m is supplied, e.g. B. a high temperature silicone oil to heat treat the corresponding parts of the bottle. Cooled fluid is supplied to the fluid channels HD , the temperature being dependent on the morphological structure of the plastic in this area after expansion.

1 shows the preform 10 on a mandrel 21 of a blow molding device 20 within the mold cavity delimited by the mold halves 16. Before it is introduced into the blow mold, the preform 10 is thermally conditioned to a temperature at which maleular orientation takes place. It is preferably heated to a temperature in the range of ITWA 75 to 110 ⁰ C; the exact temperature depends on the inherent viscosity of the polyethylene terephthalate. Before the heat treatment, the polyethylene terephthalate is essentially amorphous, ie it has a crystallinity below about 5%.

The preform 10 is first axially movable blow pin 22 stretched (Figure 2). Of the The degree of stretching or the stretching speed can be selected as desired in order to achieve a molecular orientation and to preferably initiate the crystallization caused by elongation. Of the The degree of stretching depends on the particular thermoplastic material, the temperature of the material being used desired crystallization and the degree of molecular orientation. For example it can Polyethylene terephthalate in the range of about 10 to about 500% per second, preferably about 100% per second Second. That is, a preform with a length of 2 inches will have one after one second 10.16 cm long when stretched at 100% per second.

The initial axial stretching of the polyethylene terephthalate determines the axial alignment of the molecules and initiates the crystallization caused by stretching. The axial stretching can be carried out either before or at the same time as the introduction of the blowing medium. In order to complete the blowing process, the blowing medium is introduced under pressure into the interior of the preform IC via radial passages 23 in the blow mandrel 22. For the polyethylene terephthalate of the blowing medium preferably has a pressure between about 2,067 x 10 ³ to about 4134 x 10 ³ Pa, preferably when it is introduced to an adiabatic expansion of about 2,067 ■ 10 ^3-3445 · 10 ³ Pa. Alternatively, the blowing medium can also be introduced at a pressure of about 689 · 10 ³ to 1378 · ΙΟ ³ Pa while the expansion begins; then the pressure can be increased to about 2067 x 10 ³ to 3445 x 10 ³ Pa just before the material contacts the mold wall surfaces. Molecular orientation is achieved through the expansion and, furthermore, a crystallization triggered by stretching is developed.

During the subsequent heat treatment of the container 25, the neck portion is through into the fluid channels. 14Λ circulating coolant cooled in order to maintain the essentially amorphous state of the material in this area. For the. After the heat treatment, the body is brought to a temperature in the range from about 150 to 220 ° C. A temperature of 180 ° C. at which the crystallization rate is at a maximum is particularly preferred. The prior ring can be heated to a temperature in the range of about 100 to 200 ⁰ C, depending on the during the stretching and widening in the molecular orientation caused. The bottom of the container 25 is cooled

The duration of the heat treatment can be selected according to certain variable parameters including the inherent viscosity of the material, the material thickness and the degree of crystallinity desired. It can be chosen so that it falls in the range of about 10 seconds to 10 minutes, depending primarily on the extent of the crystallinity and the passage of the crystallization through the wall thickness. _x For example B. the surface of the container 25 is rapidly heated to cause crystallization only in the vicinity of the surface. Preferably, the body of the container 25 will have a crystallinity between about 10 and 50% after the heat treatment. The embodiment shown in FIGS. 1 to 4 is preferably provided for relatively short treatment times. For longer treatment times, it is useful to cool the blown container in the blow mold and then transfer it to a separate mold cavity for the heat treatment (embodiment according to FIGS. 5 and 6).

In the case of the FIGS. 1 to 4 embodiment shown, the blowing pressure remains inside the blown Maintained container in order to avoid shrinkage of the material and the material against the To hold cavity wall. When the material is suitably thermoset, the mold halves 16 are opened and the container 25 ejected. The material should be largely self-supporting. After this Heat treatment process can also circulate coolant in channels 14B and 14C.

Embodiment according to FIGS. 5 and 6:

In this embodiment, a preform (not shown) is first placed in a blow mold made by a pair of blow mold halves 110 is formed, expanded. These are essentially the same as those in FIG. 4th shown without the thermally isolated areas; they also include coolant channels (not shown). In this embodiment, a substantially amorphous preform is first at a temperature im Area in which molecular orientation is favored, thermally conditioned. Then it will be in the from the blow mold halves 110 formed, not shown Foriuhohlraum brought, after which blowing medium under Pressure is introduced into its interior. The molding is then cooled in the glass mold halves 110 until it is is self-supporting.

When the molding is sufficiently cooled, it is placed on a blow mandrel 130 from the blow mold halves 110 in a position between two of the mold halves 141 transported around the circumference of a rotatable Tables 140 are attached. By means of a device, not shown, a plurality of Blow mandrels 130 conveyed between the blowing station and the table 140 in succession.

After the container 25 and the blow mandrel 130 have been brought into the position shown in Figure 6, the mold halves 141 around the container 25

closed to initiate the heat treatment process. At substantially the same time, the mold halves 141 of the previous mold are opened to remove the To enable ejection of a container 25 that has already been heat-treated. Then he can with these Mold halves 141 connected blow mandrel 130 are withdrawn to the blow mold to create a next preform to record. Then the turntable 140 is adjusted clockwise so that the pair of mold halves 141 the position previously occupied by the next pair 142. The container 25 in

The pair of mold halves 141 are then heat treated when the table 140 is indexed. Blowing medium under Pressure is fed into the interior of the container 25 via the blow pin 130 during the heat treatment in order to counteract material shrinkage. As can be seen, in the case of the FIG. 5 and 6 a greater crystallinity achieve by prolonging the heat treatment. The total blow molding time is used in this Embodiment not extended because the blow molding process is independent of the heat treatment.

For this purpose 3 sheets of drawings

Claims (4)

Patent claims: 1. A method of manufacturing a tubular body, a bottom, a between the Body and the bottom arranged stand ring and a neck portion having container Polyethylene terephthalate, in which a preform of amorphous polyethylene terephthalate in a Blow mold axially stretched at orientation temperature and by means of compressed air with the polyethylene terephthalate biaxially oriented towards the container is blow molded and then the internal pressure container for reinforcement the expansion-induced crystallization to a temperature higher than the orientation temperature Temperature is heated, characterized in that that during the heating the orientation in stretching and blow molding is insignificant Sections of the container, including the shark section, are cooled. 2. VerfaJsr9i according to claim 1, characterized in that that the cooling during the heating after removing the up to self-carrying cooled container from the blow mold and enclosing it in one of the outer dimensions of the container corresponding mold cavity takes place 3. Apparatus for performing the method according to claim I, with a split blow mold whose Cavity corresponds to the dimensions of the container and its mold halves fluid channels have ... characterized in that each of the mold halves (16; 141? according to the Container sections seen in the axial direction in four by means of an insulating layer each (1.1 Λ— 13Q thermal Sections isolated from one another (16/4 - 16D ^ subdivided is 4. Apparatus according to claim 3, characterized in that each of the insulating layers (13/1 - 13C) consists of glass ceramic.