A tubular object of polyethylene terephthalate

(24) Running day

PATENT AUTHORITY (62) National application number (86) International filing date (86) Filing date for European patent application (30) Priority information (11) Publication87-09-28 ^number 451 309

81-11-30

ΑΠ-17-1Π ouiriu Application received as:

80-12-10

O Swedish patent application

Q completed international patent application with number □ converted European patent application with number

80-05-29 SE 8004003-3 (71) Applicant PLM AB, Djäknegatan 16 Box 836 201 80 Malmö SE (72) Inventor K M. Jakobsen, C T. Nilsson, Skanör, Löddeköpinge (74) Ombud Magnusson G (54) Designation Transverse and axially oriented container of thermoplastic material and method and apparatus for its manufacture (56) Published publications: SE 412 549 (B29C 17/07), DE 2 340 457 (B29C 17/07) DE 2 606 355 (B29C 17/07 (57) Summary:

The invention relates to a container (21) of orientable thermoplastic material as well as a method and apparatus for providing the container.

A tubular blank of the thermoplastic material is stretched in its axis direction to form a preform which in an axial section has a contour length substantially consistent with the contour length in an axial section through the prospective container. After heating, the preform is transformed into a container form (12) into the container (21). In this way, the contour length of the stretched material is maintained by a gradual reduction in the axial length of the body the preform forms during the transformation to the container. To accomplish this, the bottom portion (11) of the biassal mold is moved toward the mouth of the future container (22). The container receives an orifice and neck portion and a container body whose material is axially oriented corresponding to the orientation of the material in the preform. In addition, at least the material in the container body has a transversely oriented orientation superposed on the axially directed. The wall thickness of the container is inversely proportional to the radius of the container. The container is very mold stable and has very good strength properties.

DB 647289

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The numbers in brackets indicate the international identification code. INID code. Letter mom pin indicates international document code

451 309

The present invention relates to a bottle or jar-like container of orientable thermoplastic material, the container having both an orifice and throat portion and a container body, wherein the orifice and throat portion and the container body include oriented material. The invention further relates to a method of forming a container by expansion of a blank wherein the blank is extended in the direction of the blank before expansion in the direction of the blank and further relates to a device for manufacturing the container in which the device comprises at least two mold parts which are movable to and from a position where the mold members together form an inner forming surface of a bi-shaped mold.

In the manufacture of containers of thermoplastic material where the material has the property of increasing the strength and stability of the material when orienting the material, it is sought that as much as possible of the container body consists of oriented material. The material is oriented by a stretching process whereby biaxially stretched material provides the best use of the available amount of material. However, especially in bottle-type containers, it is difficult to achieve stretching and consequent orientation of, for example, the neck and orifice portions and in some cases also of the centrally located bottom portions.

Swedish patent application no. SE 8004003-3 shows how, through a mechanical process, where a preform passes through one or more draw rings that reduce the wall thickness of the preform and thus also the outer diameter of the preform, it can provide an axial orientation of the material in the preform. It has been found that when the material in the preform immediately before stretching has a temperature within or below the range of the glass transition temperature (TG) of the material, the best effect is achieved. The axially oriented preform obtained in the described process is mechanically stable and the subsequent treatment of the stretched preform's conversion to the container must therefore be adapted accordingly.

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Particularly good mechanical properties are obtained from polyethylene terephthalate if the material is stretched at least about 3 times during stretching of the preform. In connection with this, an overstretching of the material easily arises, which means that when the preform is heated to the forming temperature, the material in the preform shrinks to a length corresponding to that which would be obtained at about 3 times stretch.

When converting an axially stretched preform into a container according to the above, problems arise in the form of bursting of the material if attempts are made to further stretch it beyond the stretch that the material obtained at the axial orientation of the preform described above. Therefore, in the transformation of the preform to the container, it is sought to limit the axial stretching of the preform and to essentially only allow the transformation to result in a stretch of material in the circumferential direction of the preform.

In some applications, such a combination of container length and retention aramid is required that it is not possible in the prior art to produce such a container because the material of the preform during the conversion to the container is stretched too much in the axis of the preform. The problem arises for a container of relatively large diameter in relation to the length of the container. Containers with such dimensional ratios usually exist for bottles with a volume of less than 0.5 liters.

The present invention relates to a container, method and apparatus for forming the container where stated problems are eliminated. The invention is particularly described in connection with polyethylene terephthalate, hereinafter referred to as PET, but it is in itself applicable to many other polyester or polyamide thermoplastics. Examples of such other materials are polyhexamethylene adipamide, polycaprolactam, polyhexamethylene sebacamide, polyethylene-2,6- and 1,5-naphthalate, polytetramethylene-1,2-dioxybenzoate and copolymers of ethylene terephthalate, ethylene-like phthalate and other similar phthalate.

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In a container according to the invention, the oriented material in the orifice and neck portion and the oriented material in the container body have a substantially consistent axial orientation, which is achieved by forming the container from a blank comprising substantially uniformly axially oriented material, which in the container has a corresponding in the container. axially oriented material and that axially oriented material in the retaining sheet body is additionally given one against the axial the orientation is transversely oriented, which is superimposed on the axial orientation, so that when the container is converted to the container, the blank is expanded in the circumferential direction without extending in the axis direction of the blank by the axially oriented material of the blank.

In a preferred embodiment of the invention, the central material portion and / or the orifice edge of the container consists of thermocrystallized, opaque, form-stable material or amorphous material.

In the manufacture of a container according to the invention, at the stretching of the blank in the shaft direction, a preform whose length is adapted to the dimensions of the future container is formed in such a way that the contour length of the stretched material in a cross-sectional direction through the preform formed by the blank stretches or exceeds the contour length of the stretched material in an axial section of the future container. The preform is heated to a molding temperature exceeding glass transition temperature (TG) and reshaped to the container while maintaining substantially the contour length of the stretched and heated material in an axial section through the body that arises during the preform's successive transformation into the container, which is accomplished by successive reduction. the length of said body.

In a preferred embodiment of the invention, immediately before stretching in the axis of the blank, the material has a temperature within or below the range of the glass transition temperature (TG) of the material.

Preferably, the tubular blank is stretched by passing through one or more pull rings that reduce the wall thickness of the blank while simultaneously reducing the outer circumference of the blank.

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In an embodiment where a container with a particularly high mold stability at elevated temperature is desired, the blank is selected so that the pre-heating, prior to placement in the casing mold and to a temperature exceeding the glass conversion temperature, reduces its contour length in a cut in the axis of the preform to a value not less than the contour length in an axial section of the future container.

In one embodiment of the invention, during the preform transformation, the container moves to the bottom of the preform in the axial direction of the preform and toward the orifice of the preform to assume a position in which the final internal shape of the preform is determined.

In yet another embodiment of the invention, a central material portion of the bottom of the preform obtains a reshaping and / or a reduced thickness of material, whereby the material portion is clamped between the bottom of the bias mold and a mandrel disposed within the preform.

In a device according to the invention, one of the molding parts forms the bottom part of the mold and thus the bottom of the molding surface. From a lower position (Fig. 1), the mold member is movable to and from an upper position, wherein in the lower position the inner height of the bi-mold form along the center axis of the bi-mold is adapted to the axial length of the preform before placement in the bi-mold to allow the preform's insertion therein. The upper position of the mold part (movable bottom portion of the bi-mold form) is the position immediately after completion of blowing of the preform, in which position the inner height of the bi-mold mold falls below the axial length of the preform, and in the upper position the mold part together with the other mold parts (10a, 10b) form the molding surface against which the preform is formed. to the container.

In one embodiment of the invention, the inner mandrel is terminated with a molding surface which is adapted to the shape of the bottom portion of the bias mold. When the bottom portion is in its upper position, the mandrel thereby interacts with the bottom portion for reshaping a central bottom portion of the preform and / or reducing the thickness of the bottom portion.

In yet another embodiment of the invention, the bottom part of the biassal shape is provided with a central mold part which is thermally insulated from the bottom part in general. In the central mold part are arranged channels for transporting liquid to adjust the temperature thereof

451 309 central molding forming surfaces. The bottom part is also otherwise provided with channels for transporting and adjusting the temperature of the other forming surfaces of the bottom part. Similarly, channels in the other mold parts as well as in the mandrel and grip ring halves are provided with corresponding function.

Further dependent embodiments of the invention are set forth in the dependent claims.

The invention is described in more detail in connection with three figures, where Fig. 1 shows a longitudinal section through a bias mold with axially stretched preform placed in the blow mold and with the bottom part of the bias mold in a lower position, Fig. 2 shows the corresponding longitudinal section during ongoing reforming of the preform and with the bottom part moving towards Fig. 3 shows the corresponding longitudinal section with the bottom part in its uppermost position and with the preform reshaped to the container; Fig. 4 shows a container made according to the invention.

In Figures 1-3, two mold halves 10a, b are found moving in the direction of arrows A, B to and from a position shown in the figures. The mold halves cooperate with a third mold member together to form a bi-shape mold 12 where the third mold portion forms the bottom portion of the bi-mold mold 11. Of drive means (not shown in the figures), the bottom portion is slidable between a lower position (Fig. 1) and an upper position (Fig. 3). In the upper position, the bottom part together with the mold halves forms the composite blow mold.

The bottom part is provided with a central mold part 17 thermally insulated from the bottom part in general. A plurality of channels 18 for transporting liquid are provided in the central mold portion. Channels 19 with the corresponding function are also provided in the remainder of the bottom part, as are channels 30 in the mold halves.

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Further, gripping means 13a, b, which are associated with a mandrel 15 for holding a preform 20 in its orifice 22. are provided adjacent to the upper parts of the mold halves. Also channels 31 for transporting liquid for temperature control are provided.

The mandrel 15 has a length adapted to the upper position of the bottom part 11 so that with the bottom part in its upper position formed between a lower forming surface 16 of the mandrel and the central mold part 17 of the bottom part a space of a shape and thickness determined by the desired shape and thickness of the shaped container .

Furthermore, the mandrel is provided with a main channel 14 for pressure medium which passes through the side channels 33 to the surface of the mandrel and thus to the internal volume of the preform 20.

In Fig. 1, the preform is placed in the bi-shape and the central material portion 24 of the preform in its bottom connects to the bottom part 11 of the bi-shape.

In Fig. 3 there is found a shaped container 21 and in Fig. 2 a body 23 showing the preform during transformation to the container 21.

In Fig. 4, a container according to the invention is shown in detail. The container has a neck portion 25 with an upper portion forming an orifice edge 22 '. The container body 26 itself has in its bottom part a central material portion 24. The figure denotes the radii and d) of the neck portion, respectively, with the r and d radius and the material thickness of the container body in an arbitrary plane perpendicular to the axis of the container.

The material thickness d varies in the container body with the radius of the container body r such that the ratio between the material thickness d of the container body and the material thickness dq in the neck portion is approximately equal to the ratio between the radius q of the neck portion and the radius of the container body.

In a preferred embodiment, the central material portion 24 and / or the orifice edge 22 'is thermocrystallized, opaque, shape-stable material.

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In the practice of the invention, a tubular blank is stretched in its axis direction by passing the blank through one or more pull rings that reduce the wall thickness of the blank while simultaneously reducing the outer circumference of the blank. Immediately prior to stretching, the material of the blank is at a temperature within or below the range of the glass transition temperature (TG) of the material.

The preform 20 formed during the stretching of the blank is then inserted to be heated to molding temperature in the bias mold 12. The mandrel 15 is inserted into its position inside the preform and thereby fixes the orifice 22 of the preform to the grip member 13. The bottom portion 11 of the bias mold is in its lower position. Heating medium passes through channels 18, 19, 30, 31 for setting the temperature of adjacent mold surfaces of the blow mold and preferably for heating the abutment surfaces of the gripper 13a around the preform orifice 22.

Thereafter, the interior of the preform is pressurized by means of pressure medium while the bottom portion 11 of the bias mold is moved towards the orifice portion of the preform, ie upwards in the figures. Hereby the preform expands while simultaneously reducing its axial length (cf. Fig. 2), whereby the material in the preform is stretched mainly only in the circumferential direction of the preform. When the bottom part of the biass shape has reached its upper position (Fig. 3), all of the material portions of the preform of the printing medium have also been brought into contact with the inner forming surfaces of the biag mold and the preform has been transformed to the container 21.

In some application examples, the internal pressure of the shaped container is maintained for a certain period of time so that secure contact with the bias form is obtained. Thus, the forming surfaces of the bias mold have a temperature in the range of 110 DEG-18 DEG C. preferably 130 DEG-150 DEG C., whereby the internal stresses in the material are released and at the same time a certain thermal crystallization takes place in the material. In this way, the container is mechanically stabilized in its shape and is capable of being reheated without any major change to the temperature at which thermostabilization occurred.

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When the thermostabilization of the container is completed, the mold halves are opened, the bottom part of the bias mold is moved to its lower position and the shaped container is removed from the bias mold.

In some applications, the material is cooled in the preform and thus the central bottom portion of the container, i.e., the material which is reshaped and / or reduced in thickness between the molding surface 16 of the mandrel 15 and the central mold portion 17 of the bottom portion 11 of the bias mold, thereby obtaining a container whose central bottom portion consists of amorphous material. In other applications, the material is heated in a manner similar to that just described in connection with the thermostabilization of the container, in that the forming surface 16 of the mandrel 15 has a temperature in the region within which the amorphous material crystallizes, preferably a temperature of 130-160 ° C. In this case, the central bottom portion of the container is formed into a thermocrystallized, opaque, shape-stable material region.

In some applications, where the requirements for mold stability of the molded container at higher temperature are not quite so great, the material in the preform during stretching is also stretched in the axis direction of the preform. However, the stretch is relatively small and is allowed at PET to correspond to a maximum of about 30 7, extension of the material. The axial stretch ratio according to the invention is governed by the length of the vertical movement of the bottom portion 11 of the bias mold.

The invention is described above in connection with a bias mold whose bottom part during the preform conversion to the container is moved in the axis direction of the bias shape. It is to be understood that the invention is not limited solely to the embodiment described but the inventive idea as such can be realized, for example, by means of a fixed-bottom box liner mold and where the gripping ring halves together with the mandrel are moved in the axial direction of the bi-mold during the reforming of the preform.

A container according to the invention has in the neck portion 25 a crystallization located in the range of about 5-15. In the embodiment where the central mold portion 17 holds the central bottom portion 24 at a temperature which does not cause thermally conditioned crystallization or

451 309 only slightly (for PET below about 100 ° C), an amorphous central bottom portion 24 having a crystallization less than 5 Z is obtained. In the case that the central mold portion 17 holds the material at crystallization temperature (for PET about 140 ° C), a crystallized, opaque, particularly shape-stable central material region with a crystallization exceeding about 10%. The corresponding crystal line ratio applies to the edge of the orifice 22 depending on whether it is cooled or heated to newly specified temperature ranges by the mandrel 15 and / or the gripping means 13a, b.

In addition to the above description, the invention is also apparent from the following claims.

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