DE3729166C2 - - Google Patents

Description

The invention relates to a method for producing a semi-crystalline, biaxially oriented, heat-set Plastic container according to the preamble of patent claim 1.

In such a known method (US-PS 40 39 641) is heated to orientation temperature Polyethylene terephthalate preform enclosed in a blow mold and in this under biaxial orientation to finished container inflated. By contact with the blow mold walls heated to heat setting temperature the container is heat-set and thereby by the internal pressure the blowing fluid prevented from shrinking. Subsequently can either the blow mold cooled to about 60 ° C and the Be removed container. The cooling of the container can but also be made so that a pressurized Coolant introduced into the container while the Blowing fluid is displaced from the container. Once the cooled Container is dimensionally stable, for example at 40 ° C, it can be taken from the blow mold. As a coolant serves a provided for filling in the container beverage like beer, so that even after opening the tuyere the liquid still exerts a cooling effect on the container. To one avoid strong heating of the liquid to be filled the blow mold should be opened as soon as possible.

In another known method (US-PS 44 76 170) is also a preform of polyethylene terephthalate in a blow mold blown at orientation temperature and thereby  biaxially stretched and by contact with the blow mold walls to the heat setting temperature in the range of about 200 to 250 ° C brought and the container heat-set, whereby he under Internal pressure is maintained to avoid shrinkage. In the mold is cooled to a temperature of the container above 100 ° C, where it is dimensionally stable, so that after Pressure relief of the tank inside the blow mold open and the container can be removed. Besides, this is also out of it known to open the mold immediately after thermosetting, wherein the internal pressure must be sufficiently high. The cooling then takes place outside of the blow mold by blowing with air. This achieves a higher shrinkage initial temperature, if from the heat-setting temperature in the tuyere a quenching temperature of over 100 ° C is cooled.

For cooling plastic blow molded containers without biaxial orientation and heat setting, it is also known (US-Re 28 497) that a cooling fluid circulates through the container, So continuously introduced into the container and discharged from this becomes. As a cooling fluid is liquid carbon dioxide, the evaporated when introduced into the container. Cooling in the Form takes place until the container is self-supporting, whereupon the internal pressure is reduced to atmospheric pressure and the Container is removed from the blow mold.

The invention has for its object to provide a method of eingangsilden type so that the cycle time considerably shortened for the production of heat-fixed containers becomes.

The object is achieved by the features of the claim 1 solved.

According to the invention thus the container is removed from the blow mold, if the average temperature of the container so far is reduced, that he due to the internal pressure of the cooling fluid so far is self-supporting that the container does not collapse and also not unduly expands when the blow mold is opened. Subsequently, the circulation of the cooling fluid  continued through the container until it has cooled so far that he is self-supporting and in this state no essential Shrinkage learns more. Then that will be circulating the cooling fluid terminated and the container released.

According to the invention, the production time of the container is essential shortened. The method according to the invention is suitable also in particular for non-cylindrical, for example oval Container, as well as for complicated container shapes, for example Container with two or more cylindrical sections different cross sections or for container shapes, the cylindrical and oblique sections and grooves, ribs u. ä. respectively. The inventive method can be in known Perform blow molding, so that the construction and maintenance are low and easy to carry out the adjustments are.

Advantageous developments of the method according to the invention are characterized in the subclaims.

The cooling fluid consists of liquid carbon dioxide or liquid nitrogen or a mixture of water vapor and Air at zero or sub zero temperature. As a cooling fluid liquid carbon dioxide is preferred, with a superatmospheric Pressure is introduced and within the Tank relaxed, the combination of the temperature difference between the container and the carbon dioxide and the heat of vaporization of the carbon dioxide at the transition from the solid or liquid to the gaseous state in the Container in which a low pressure prevails, to cool is exploited. During cooling, the pressure is in the Tank a little larger than the atmospheric pressure.

If the cooling fluid consists of a mixture of water mist and Lower, it expands in the tank and improves the cooling by first getting a solid state like snow or ice, followed by evaporation in the gaseous Condition occurs. If the cooling fluid consists of liquid nitrogen, so also in the evaporation of the liquid in the  used gaseous state resulting cold for cooling.

The inventive method is in polymers applied, which can be biaxially oriented when they blown at orientation temperatures and subsequently be heat-set at higher heat-setting temperatures, thermally stable around the hollow article produced to make and provide improved barrier properties.

The inventive method and the product is specially made with polymers of polyethylene terephthalate (PET), which has an inherent viscosity of have at least 0.6 polyethylene terephthalate polymers, the repeating ones useful for the present invention Include ethylene terephthalate units, with an excess on small amounts of ester-forming components and copolymers of ethylene terephthalate, wherein up to 10 mole percent of the Butane-1,4-diol; diethylene glycol; Propane-1,3-diol; Polytetramethylene glycol); polyethylene glycol; Poly (propylene glycol); 1,4-hydroxymethylcyclohexane and the like selected are substituted for the glycol content in the processing of Copolymers, or isophthalene; Naphthalene 1,4- or 2,6-dicarboxyl; adipic; Sebacyl; Decane-1,10-dicarboxylic acids, and the like, replaced for up to 10 mole percent of the acid moiety (Terephthalic acid) in the preparation of the copolymer.

The polyethylene terephthalate polymer may, of course, be various Contain additives that are not contrary to the polymer act. Some such additives are stabilizers, Antioxidants or shielding agents ultraviolet Light, sprayable, additives to the polymer degradable or flammable, and dyes or pigments. Furthermore, means for cross-linking or branching, as described in US Patent 41 88 357  are introduced in small quantities to the melt strength of polyethylene terephthalate.

The method is also applicable to multilayer preforms, the an orientable, thermofixable polymer and other polymers include the desirable barrier properties wherein the orientable, thermofixable Polymer a major part of the total weight at least 70%. Typical examples of multilayer preforms are preforms made Polyethylene terephthalate and copolyester; polyethylene terephthalate, Nylon and copolyester; polyethylene terephthalate, Adhesive, nylon, glue and polyethylene terephthalate.

The method is also applicable to blends of polyethylene terephthalates with polymers that are desirable Have barrier properties, wherein the polyethylene terephthalate a large proportion of the total weight, preferably at least 70% of the total weight.

The here in the claims and the description used Expression of polyethylene terephthalate includes those listed above Polyethylene terephthalate containing materials.

An embodiment of the invention is described below explained in detail the drawing. It shows

Fig. 1 is a schematic drawing showing the successive steps in the inventive method,

FIG. 2 is a partial schematic view of part of a device used in the method . FIG.

Fig. 3 shows an enlarged section of a nozzle, as used in the apparatus,

Fig. 4 shows a section along the line 4-4 in Fig. 3,

Fig. 5 is a side view of a container which could be made according to the invention,

Fig. 6 shows the bottom view of the results shown in Fig. 5 container,

Fig. 7 is a schematic drawing of the successive steps of a modified method of the invention.

It is important to introduce the cooling fluid that it reaches the entire inner surface of the container may, except possibly at the mouth, and it preferably so uniformly introduce that a uniform Cooling is achieved. That is why the location of the nozzle, through the cooling fluid is introduced as important as the construction the nozzle.

Referring to FIGS. 2, 3, 4, a nozzle N has a first number of circumferentially disposed apertures 10 that are radially aligned, a second group of circumferentially disposed apertures 11 that are radially downwardly and axially directed toward the neck of the container C , and a third group of circumferentially disposed openings 12 directed radially and axially in an axial direction toward the base of the container.

Referring to Fig. 2, the nozzle n is seated on a hollow stretching rod 13 which can be inserted into the mold through the portion of the mold which forms the neck by cooperating a cylinder 14 with a piston 15 on the rod 13 . The blowing pressure is supplied through a three-way valve 16 to pass the blowing fluid such as air or nitrogen through a passage 17 through a space 18 to the hollow rod 13 and the nozzle N to inflate the preform P and form the container C. At the same time, the nozzle N is guided to the desired position in the container C. On the other hand, the nozzle N at the end of the rod 13 can be used as a stretching rod to axially stretch the preform even before the blowing fluid is introduced or simultaneously with introduction of the blowing fluid, after which the rod is pulled withdrawn, around the nozzle N to its desired location to bring inside the container C to cool the container C. The blowing fluid is first applied at a low pressure, e.g. 70 to 200 psi, and then the blowing fluid is applied at a higher pressure, e.g. 150 to 350 psi to maintain contact of the container with the surface of the blow mold. After crystallization is complete or the time for heat setting has expired, the valve 16 sucks the blowing fluid through the channel 17 into the atmosphere. The cooling fluid, such as carbon dioxide, is fed from a source S through a conduit 19 and a solenoid valve 20 to the channel in the hollow rod 13 and the nozzle in the blown container C , and is continuously sucked through the channel 17 via the periphery of the nozzle N. The interior of the rod 13 is provided with a plastic tube 21 of nylon or similar material to avoid the freezing or blocking of the channel in the hollow rod 13 .

In the manner of the method, as shown in Fig. 7, the mold M ₁ is a tripartite shape consisting of the mold sections 40 , which close to a bottom part of the mold 41 . The bottom part 41 is intended to form the bottom of the container. In this method, the mold bottom by a liquid cylinder 42 with a piston rod 43 is axially movable, so that when the mold is opened M ₁ and the cooling fluid is continuously introduced into the container, there circulated and continuously removed or sucked, the bottom of the container in its position from the bottom part 41 of the mold as shown in section D in Fig. 7, is held. After the introduction of the cooling fluid is completed, the bottom part 41 is withdrawn axially outward, and the container is released by opening the mouth mold 22 .

This method uses a movable bottom mold then has a special benefit, where the ground the container has a shape that the container is free can.

It can be seen that the introduction of carbon dioxide or similar cooling fluids causes the average temperature the container sinks while the mold is closed is. When the mold is opened, the positive prevents Pressure of the continuously flowing carbon dioxide not only that the container collapses in itself, but in addition It continues to cool the container from the inside and thereby further reduces the average temperature of the container until it reaches a stable state. Where the temperature for heat-setting, usually 200 ° or higher, is also the average temperature of the container before the opening of the mold necessarily higher, and if the excess pressure of carbon dioxide and the Cooling last a longer period of time, there is the Possibility that the container grows in volume easily. To avoid this growth must, if necessary is the duration of the supply of carbon dioxide after the Opening of the mold can be reduced or controlled, so that the cooling process continues until the container becomes self-supporting is, and he finishes before the container undesirable growth. Another reason, the cooling time to keep small, is that on the other hand the Cycle time increases and the cooling fluid consumption significantly increases, which adversely affects productivity and costs. It must be noted that the In any case, growth or expansion in the volume is minimal and that the above considerations are only applied there where it is desirable that the container not in volume from that of the blown container different.  

The following parameters provide satisfactory results for polyethylene terephthalates:

Orientation temperature | 80-110 ° C Heat setting temperature 120-250 ° C Heat-setting time 0,5-10 sec. cooling time 1.0-10 sec. Mold opening delay 0.5-9.5 sec.

A preferred parameter range includes a heat setting temperature, which is between 180 and 230 ° C, a Heat setting time, which is between 1 and 5 seconds, a mold opening delay of between 0.5 and 5 seconds lies, and a cooling after the mold opening, the between 0.8 and 1.2 seconds.

Referring to Figs. 5 and 6, such containers 30 include e.g. B. eight vertical grooves 31 , three horizontally extending ribs 32 and a frusto-conical shoulder portion 33rd

In the following test results, the container had a shape as shown in Figs. 5 and 6, and the suction of the blowing fluid and the introduction of the cooling fluid were carried out simultaneously. The mold opening delay time was measured from the beginning of sucking out the blowing fluid and introducing the cooling fluid. The bottom temperatures of the mold were lower, so that the thicker bottom of the container was less heat-set.

In the following test results, the polyethylene terephthalate container was prepared with an IV of 0.80. The axial draw ratio was 1.6 ×, and the Umfassungsreckverhältnis was 4.8 × to 5.3 × in the region of the grooves 31 ; it was in the range of 3.4 × to 5.3 × in the region of the ribs 32 ; it was in the range of 3.4 × to 3.66 × at the shoulder portion 33 .

To demonstrate the importance of nozzle positioning in the fabrication of complex containers, tests were conducted where containers of FIGS. 5 and 6 were made having a height of 9½ inches and an overflow volume without shrinkage of about 1490 cc had.

Table A below summarizes the results:

Table A

nozzle position

It can be seen that when the nozzle position is between 2 and 3½ inches off the ground, containers with one good dimensional stability and reduced shrinkage after blow molding (Overflow volume) are produced. That's the way it is necessary to build and position the nozzle so that the coolant cools all sections of the container.

Table B comprises a number of tests together with different mold opening delay times and carbon dioxide cooling times were made.  

Table B

Table B (continued)

It can be seen from Table B, bottle number 4B, that the container obtained is immensely coincidental when the Mold opening delay and the cooling time are the same. Farther occurred at the bottle numbers 4B, 7B, 10B Kollapse or Shape loss on when the difference between the mold opening delay time and the carbon dioxide supply time less than 0.5 seconds. For bottle 15B was the Combination of mold opening delay and cooling time is not sufficient to cool the container until it self wearing. This can be remedied by the mold opening delay time is reduced, as with bottle number 11B, compared with bottle number 10B, or Bottle number 8B compared to bottle number 7B. on the other hand the cooling time can be increased, as with the Bottle numbers 14B and 16B compared to bottle number 15B, is shown. The remaining containers were in the form-fidelity, the desired overflow volume and the general Appearance satisfactory.

Table C shows a number of tests in which the Mold opening delay and the CO₂ supply time are the same and at different thermofixation or crystallization temperatures.  

Table C

All containers were very deformed, collapsed and not acceptable.

It can be seen that in each example the resulting Container strongly deformed and collapsed in itself and can not be sold. Additional tests have shown that comparable containers with a substantial Loss of dimensional stability at lower thermofixation temperatures occur, with the mold opening delay and the Cooling time are the same.

It can be seen from this that it is essential that the Supply of carbon dioxide continues after the mold is opened was to get satisfactory results.

Table D below summarizes the property obtained in typical examples of the container shown in Figs. 5 and 6:

Table D

Properties in refrigerated containers

Heat setting temperature = 228 ° C
Heat setting time = 5 seconds
CO₂ time = 5 seconds

It can be seen that the mechanical properties and the improved density is sufficient.

If the inherent viscosity is included herein the viscosity as measured at a 60/40 weight ratio Phenol / tetrachloroethane solution at 25 ° C. The concentration  was determined by the method as described in ASTM 1505 is titled "Density Gradient Technique".

The mechanical properties were measured as in the ASTM standard D-638.

The following Table E shows the results of shrinkage initial temperatures. It can be seen that the initial shrinkage temperature is significantly increased by the method of making a container shown in Figs. 5, 6, compared to the same container made without heat setting:

Table E

Shrinkage starting temperature

Heat setting temperature = 228 ° C
Heat setting time = 5 seconds
CO₂ duration = 5 seconds

The shrinkage initiation temperature involved herein became as with Brady and Jabarin "Thermal Treatment of Cold-Formed Poly (Vinyl Chloride) Polymer Engineering and Science ", Pages 686-90 of issue 17, no. 9, September 1977, except that the specimens from the side walls of the bottles were cut out. The cut samples were not thermally treated before the tests.  

Table F shows the results of the tests, those at lower Heat setting times were performed.

Table F

It can be seen that satisfactory containers together be obtained with lower heat setting times.

It can be seen that a method of preparation a biaxially oriented, heat-set container with a high shrinkage initial temperature was invented.

In various tests of the heat setting process of the invention it became evident that the received container can be cooled quickly below more than 100 °, you can handle it easily and from people who perform the procedure, can be touched.  

Observations in accordance with the widespread Stray light test were performed, show that the containers, in accordance with these procedures were prepared, a more uniform crystalline size distribution in the body of the container, better than them from previously performed thermofixing, the long Time periods for cooling the container after thermosetting need to be obtained. One must believe that due to this more uniform crystalline size distribution fast quenching or cooling in accordance achieved with this method.

In case the containers are complex or freestanding Soils, a mold bottom is provided, which is in contact remains with the bottom of the container when the mold is opened and the cooling fluid continues into the interior of the container is introduced while the mold bottom contact with the ground the container has. The movable mold bottom can also be used for containers be used with a hemispherical bottom, to stabilize the container while the mold is open is and the cooling fluid is supplied.

Claims (5)

A method of making a semi-crystalline, biaxially oriented, heat-set plastic container from a hollow preform having an open end and a closed end,
in which the open end of the preform, having a temperature within its molecular orientation range, is detected,
wherein the preform is enclosed in a hot blow mold having heat set temperature,
wherein the preform in the blow mold is expanded by a blowing fluid to the vessel to biaxially orient the preform and bring it into close contact with the blow mold and to maintain contact by the internal pressure of the blowing fluid for a time sufficient to to cause a partial crystallization of the plastic,
in which subsequently the blowing fluid is discharged and at the same time a cooling fluid is introduced,
in which the container is cooled, taken out of the blow mold and further cooled outside the blow mold by means of the cooling fluid, characterized
in that the cooling takes place by means of a cooling fluid which changes its state of aggregation upon introduction into the container and which circulates continuously through the container,
that the removal from the blow mold takes place at a time at which the collapse of the container due to the cooling fluid pressure is avoided, and
that the circulation of the cooling fluid is continued until the container is self-supporting. 2. The method of claim 1, comprising a nozzle for insertion the cooling fluid, characterized in that the insertion  the cooling fluid radially and axially on all inner surfaces directed directed to the container. 3. The method according to any one of claims 1 or 2 when using polyethylene terephthalate for the preform, characterized in that the method is carried out with the following parameters: Orientation temperature | 80-110 ° C Heat setting temperature 120-250 ° C Heat-setting time 0.5-10 s cooling time 1-10 s Mold opening delay 0.5-9.5 s 4. The method of claim 3 with the following parameters: Heat setting temperature | 180-230 ° C Heat-setting time 1-5 s Mold opening delay 0,5-5 s Cooling time after opening the blow mold 0.8-1.2 s 5. The method according to any one of claims 1-4, characterized by the use of liquid carbon dioxide, of liquid Nitrogen or a mixture of water mist and air with Zerotemperatur for the cooling fluid.