GB2195287A

GB2195287A - Method and apparatus for making a partially crystalline, biaxially oriented heat set hollow plastic container

Info

Publication number: GB2195287A
Application number: GB08718440A
Authority: GB
Inventors: Prakash R Ajmera
Original assignee: Owens Illinois Plastic Products Inc
Current assignee: Graham Packaging Plastic Products Inc
Priority date: 1986-09-22
Filing date: 1987-08-04
Publication date: 1988-04-07
Anticipated expiration: 2007-08-04
Also published as: FR2604118A1; AU7832587A; GB2195287B; ZA876266B; JPH0535666B2; CA1288913C; JPS6384918A; GB8718440D0; DE3729166C2; AU580219B2; FR2604118B1; DE3729166A1

Description

1 GB2195287A 1

SPECIFICATION

Method and apparatus for making a partially crystalline, biaxially oriented heat set hollow plastic container This invention relates to making hollow biaxially oriented heat set partially crystalline articles and particularly articles made of poly(ethylene) terephthalate.

Background and Summary of the Invention

It has heretofore been known that the thermal stability and barrier properties of oriented blow 10 molded containers of poly(ethylene) terephthalate are significantly increased by heat setting.

Typical processes for heat setting are shown in United States Patents 4, 476,170, 4,512,948 and 4,522,779.

In United States patents 4,476,170 and 4,512,948, there is disclosed an article and a process of making an oriented and heat set blow molded container of poly(ethylene) terephthalate. In the 15 process, a preform preheated to a temperature suitable for orientation is biaxially stretched in a blow mold and then while the hollow container is still in contact with the blow mold walls, the article is raised to a higher heat setting temperature preferably in the range of 200'250'C.

(except for the neck) thus heat setting the container, and while the container is still at a shrinkage resisting pressure exceeding atmospheric, it is cooled in the same mold to a tempera- 20 ture at which is it maintains its shape when not pressurized but not below 100'C. It is also particularly disclosed that this cooling step can be done in the air outside the mold while maintaining internal pressure. According to these patents, when the heat setting temperature of the hot mold ranges from 220-250'C and the quenching temperature is not below 100'C, higher onset-of-shrinkage temperatures are obtained.

In United States Patent 4,522,779, there are disclosed improved plastic containers and a process for their production.

2 0 In the first embodiment, a container is blow molded in a first hot blow mold, then reblown to a larger size in a second cold mold of larger volume than the first hot mold. Such containers are stated as having improved physical properties, particularly very high hoop yield stresses. How- 30 ever, the utilization of a larger volume cold mold substantially reduces the thermal stability. In the second embodiment, a container is blow molded in a hot blow mold, then reblown to a larger size in a second hot blow mold where it is blown to the confines of of the second mold and the container is then removed from the second hot mold and transferred to a third cold mold and cooled to room temperature while maintaining internal pressure. In a further embodi- 35 ment, the container is blow molded in a first hot mold, reblown in a second hot mold, and thereafter the second mold is cooled to cool the container.

United States Patent 4,385,089 (British Patent Specification 1,604,203) is directed to heat set biaxially oriented hollow articles and states that the preform or parison should be heated at least to biaxially oriented temperature and maintained in closed contact with a hot mold which is at a 40 temperature of up to 40'C above the minimum oriented temperature. In one embodiment, the resultant molded hollow article is moderately cooled causing a temperature drop of 10-30'C by introducing cooling vapor or mist into the hollow article, interrupting the cooling vapor, and opening the mold. In another embodiment, the heat set article is allowed to shrink freely and then reblown in the same hot mold or in a separate cooled mold. The patent calls for a heat 45 setting temperature of 40'C above the orientation temperture limits thermal stability and barrier properties from heat setting.

According to this patent, the temperature of the hot mold should be maintained between 30 and 50'C above the minimum orientation temperature of the plastic material. Otherwise, it is stated there are numerous disadvantages including lowering of the production rate, the danger of 50 the appearance of major distortion and major shrinkage on mold release, the disadvantage inherent in heating metal molds to very high temperatures and keeping them at such temper tures, and the danger of crystallization which would cause a loss of transparency. Further, in accordance with this prior patent, excessive shrinkage is to be avoided and generally the temperature drop of 10 to 30'C should be made. Accordingly, such a method precludes obtaining a degree of heat setting which would produce thermal stability at higher temperatures as may be required in filling the container with various products. In addition, such a method will preclude obtaining the higher degrees of crystallinity and resultant high barrier properties which are required for some products.

United States Patent 4,039,641 discloses a process for producing a heat set biaxially oriented 60 poly(ethylene) terephthalate bottle filled with a liquid wherein a. parison is expanded in a mold which is at a temperature in the range of 130 to 220'C and maintained in contact with the mold by a gas such as pressurized carbon dioxide and the crystallized bottle is cooled by displacing the pressurizing gas with a cooling liquid which is cooled to about 0 to 5'C. The liquid may be liquid to be packaged in the container. Such a method substantially reduces the cycle time 65 2 GB2195287A 2 because of the need to introduce the liquid and thereafter remove the liquid, in the case where the liquid is not that to be packaged in the container. Moreover, utilizing a liquid within the container to cool the container limits the amount of heat that can be extracted from the container because it has a low coefficient of heat transfer. Furthermore, the low coefficient of heat transfer takes a longer time to extract the heat. In addition, filling the container with a finite amount of liquid equal to the volume of the container limits the amount of heat which can be extracted from the container to the amount of heat that can be transferred to this finite amount of liquid.

United States Patent RE. 28,497 discloses a method and apparatus for reducing mold cycle time in a conventional blow molding method wherein a heated parison is expanded by a gas 10 such as gaseous carbon dioxide in a blow mold and thereafter subsequently internally chilled by a liquid carbon dioxide.

The article is cooled until it is self-sustaining, the article is vented to atmospheric pressure, the mold is opened, and the article is removed from the mold.. The patent does not relate to biaxially oriented articles or heat setting of biaxially oriented articles.

None of the prior art recognizes or teaches that it is necessary to continue the cooling by circulating liquid carbon dioxide after the mold is opened in order to obtain self-sustaining biaxially oriented heat set containers, as in the present invention.

Accordingly, among the objectives of the present invention are to provide a method and apparatus for making partially crystalline, biaxially oriented heat set hollow plastic containers which has a significantly lower cycle time; which permits heat set containers to be made that have complex configurations including oval containers; which involves low capitalinvestment; which is easy to maintain; and which involves the use of lower cost tooling.

In accordance with the invention, the method and apparatus for making a partially crystalline, biaxially oriented heat set hollow plastic container from a hollow parison having an open end and 25 a closed end comprising engaging the open end of a plastic parison which is at a temperature within its molecular orientation temperature range, enclosing the hot parison in a hot mold, the mold being at heat setting temperature, expanding the plastic parison within the hot mold by internal pressurization to induce biaxial orientation of the plastic parison and force the plastic parison into intimate contact and conformance with the hot mold and to maintain contact by such internal pressurization between the mold and the biaxially oriented container for a time sufficient to induce partial crystallization in the biaxially oriented container, exhausting the blow molding fluid while continuously introducing a cooling fluid such as liquid carbon dioxide into the biaxially oriented container and continuously removing the cooling fluid from the container while the hot mold is closed for a period of time, opening the hot mold while continuing to introduce, circulate and remove coolant fluid for a predetermined period of time until the container is cooled sufficiently to prevent significant shrinkage and finally releasing the container.

Description of the Drawings

Fig. - 1 is a diagrammatic view showing of the successive steps in the method embodying the 40 invention.

Fig. 2 is a partly schematic view of a portion of an apparatus utilized with the method.

Fig. 3 is an enlarged sectional view of a nozzle utilized in the apparatus.

Fig. 4 is a sectional view taken along the line 4-4 in Fig. 3.

Fig. 5 is an elevational view of a container which may be made in accordance with the 45 invention.

Fig. 6 is abottornview of the container shown in Fig. 5.

Fig 7 is a diagrammatic view of the successive steps in a modified method embodying the invention.

Referring to Fig. 1, the method for making a partially crystalline, biaxially oriented heat set hollow plastic container from a hollow parison having an open end and a closed end comprises engaging the open end of a plastic parison P by a neck clamp which has been heated (step A) at a temperature within its molecular orientation temperature range, enclosing the hot parison in a hot mold M, the mold being at heat setting temperature, expanding the plastic parison within the hot mold M by internal pressurization to induce biaxial 55 orientation of the plastic parison and force the plastic parison into intimate contact and confor mance with the hot mold M and to maintain contact by such internal pressurization between the mold M and the biaxially oriented container for a time sufficient to induce partial crystallization in the biaxially oriented container (step B), exhausting the blow molding fluid while continuously introducing a cooling fluid such as liquid 60 carbon dioxide into the biaxially oriented container while continuously circulating and continuously removing the cooling fluid from the container, while the hot mold is closed for a period of time (step Q, opening the hot mold while continuing to introduce coolant fluid and while continuously circulating and continuously removing the cooling fluid from the container for a predetermined Z1 J 3 1 GB2195287A 3 period of time until the container is cooled sufficiently to prevent significant shrinkage (step D) and finally releasing the container.

It has been found to be important to introduce the cooling fluid medium such that it is applied over the entire inner surface of the container, except possibly for the finish, and preferably uniformly so that adequate cooling is achieved. Thus, the position of the nozzle through which the cooling medium is introduced is important as well as the construction of the nozzle.

Referring to Figs. 2, 3, 4, a preferred nozzle N comprises a first plurality of circurnferentially spaced orifices 10 that extend radially, a second set of circurnferentially spaced orifices 11 that extend downwardly radially and axially toward the neck of the container C and a third set of 10 circurnferentially spaced orifices 12 that extend radially and axially in an axial direction toward the base of the container.

Referring to Fig. 2, the nozzle N is positioned on a hollow stretch rod 13 which is adapted to be moved within the mold through the neck forming portion of the mold by operation of a cylinder 14 cooperating with a piston 15 on the rod 13. Blowing pressure is provided through a 15 three way valve 16 for supplying blowing fluid such as air or nitrogen through passage 17 to the space 18 about the hollow rod 13 and nozzle N to blow the parison P and form the container C. At this time, the nozzle N is moved to the desired position within the container C.

Alternatively, the nozzle N may be used at the end of rod 13 as a stretch rod to stretch the parison axially prior to introducing the blowing fluid or simultaneously with introducing the blowing fluid after which the rod is retracted to bring the nozzle N to the desired position within the container C for cooling the container C. The blowing fluid is first applied at a lower pressure, for example, 70 to 200 p.s.i, and then the blowing fluid is applied at a higher pressure, for example, 150 to 350 p.s.i., to maintain contact of the container with the surface of the mold.

After the completion of the crystallization or heat setting time, the valve 16 is activated to exhaust the blowing fluid through passage 17 to the atmosphere. The cooling fluid such as carbon dioxide is provided from a source S through a line 19 and solenoid operated valve 20 to the passage in the hollow rod 13 and nozzle into the blown container C and is exhausted continuously about the periphery of the nozzle N through passage 17. A plastic tube 21 of nylon or the like is provided on the interior of rod 13 to minimize the freezing or blockage of the 30 passage in the hollow rod 13.

As used herein, cooling medium comprises liquid carbon dioxide, liquid nitrogen, or combined mixture of water vapor and sub-zero temperature air. A preferred cooling medium comprises liquid carbon dixoide which is introduced at super atmospheric pressures and expands from the openings or orifices in the nozzle N, utilizes the combination of the temperature differential between the container and the carbon dioxide and the latent heat of evaporation of carbon dioxide from either its liquid or solid state to its gaseous state in the lower pressure existing in the container. During the cooling, the pressure within the container is slightly greater than atmospheric.

If the cooling medium is combined water mist and sub-zero air, passage through the openings 40 of a nozzle N will also result in expansion and facilitate cooling by first forming a solid state of snow or ice followed by evaporation to the gaseous state. If the cooling medium is liquid nitrogen, the heat transfer or cooling action is by heat transfer due to latent heat evaporation from the liquid to the gaseous state followed by temperature differential between the gaseous state and the container.

In operation, the steps comprise:

engaging the open end of a plastic parison P which has been heated (step A) at a temperature within its molecular orientation temperature range, enclosing the hot parison in a hot mold M, the mold being at heat setting temperature, expanding the plastic parison within the hot mold M by internal pressurization to induce biaxial 50 orientation of the plastic parison and force the plastic parison into intimate contact and confor mance with the hot mold M and to maintain contact by such internal pressurization between the mold M and the biaxially oriented container for a time sufficient to induce partial crystallization in the biaxially oriented container (step B), exhausting the blow molding fluid while continuously introducing a cooling fluid such as liquid 55 carbon dioxide into the biaxially oriented container while continuously circulating and continuously removing the cooling fluid from the container, while the hot mold is closed for a period of time (step C), opening the hot mold while continuing to introduce coolant fluid while continuously circulating from the container for a predetermined period of 60 to prevent significant shrinkage (step D) and and continuously removing the cooling fluid time until the container is cooled sufficiently finally releasing the container (step D). In the form of method shown in Fig. 7, the mold M, is a three sectional mold comprising mold sections 40 which close about a mold base section 41. The mold base section 41 is configured to form the bottom of'the container. In this method, the mold base is movable axially 65 4 GB2195287A 4 by a fluid cylinder 42 through a piston rod 43 so that when the mold M, is opened and the cooling fluid is continuously introduced into the container, circulated and continuously removed or exhausted, the base of the container is held in position by the mold base section 41 of the mold as shown at station D in Fig. 7. After the completion of the introduction of the coolant fluid, the mold base section 41 is retracted axially outwardly and the container is released by opening the neck clamp 22.

This method of using a movable base section has particular utility where the container base has a configuration such that the resultant container is free standing.

It can thus be seen that the introduction of carbon dioxide or similar cooling fluid functions to reduce the average temperature of the container while the mold is closed. When the mold is 10 opened, the positive pressure of the continuously flowing carbon dioxide not only prevents the container from collapsing but, in addition, continues the cooling of the container from the interior and thereby continues to reduce the average temperature of the container until it achieves a selfsustaining condition. Where the heat setting temperature, on the order of 200C or higher, the average temperature of the container upon opening of the mold is necessarily higher, and if the 15 positive pressure of the carbon dioxide and the time of cooling continues for an excessive period of time, there is a possibility that the container may slightly grow in volume. In order to obviate such growth, if it is necessary, the time of application of the carbon dioxide after opening of the mold may need to be reduced and controlled so that the cooling continues until the container is self-sustaining and is terminated before any undesirable growth is achieved. A further reason for 20 minimizing the cooling time is that otherwise the cycle time is increased and the consumption of cooling fluid is substantially increased, thereby adversely affecting productivity and costs. It should be understood that the growth or expansion in volume in any event is minimal and the above considerations are applicable only where it is desired that the container have substantially no change in volume from that of the blown container.

The process of the present invention is applicable to polymers which are capable of being biaxially. oriented when blown at orientation temperatures and subsequently heat set at higher heat setting temperatures to make the resultant hollow article thermally stable and provide improved barrier properties.

The process of the present invention, as well as the product, is especially concerned with polymers of poly(ethylene) terephthalate having an inherent viscosity of at least 0.6. Poly(ethyl ene) terephthalate polymers useful in the present invention include repeating ethylene terephtha late units with the remainder being minor amounts of ester-forming components and copolymers of ethylene terephthalate wherein up to about 10 mole percent of the copolymer is prepared from the monomer units selected frombutane-1,4-diol;diethylene glycol; propanel,3-diol; poly tet- 35 ramethylene glycol); poly ethylene glycol); poly(propylene glycol); 1,4- hydroxymethylcyclohexane and the like, substituted for the glycol moiety in the preparation of the copolymer, or isophthalic; naphthalene 1,4- or 2,6-dicarboxylic; adipic; sebacic; decane-1,10dicarboxylic acids, and the like, substituted for up to 10 mole percent of the acid moiety (terephthalic acid) in the preparation of the copolymer.

Of course, the poly(ethylene) terephthalate polymer can include various additives that do not adversely affect the polymer. For instance, some such additives are stabilizers, e.g., antioxidants or ultraviolet light screening agents, extrusion aids, additives designed to make the polymer more degradable or combustible, and dyes or pigments. Moreover, cross-linking or branching agents such as are disclosed in United States Patent No. 4,188,357 can be included in small amounts 45 in order to increase the melt strength of the poly(ethylene) terephthalate.

The process is also applicable to multilayer parisons comprising an orientable heat settable polymer and other polymers which provide desirable barrier properties wherein the orientable heat settable polymer comprises a major portion of the total weight, preferably at least 70%.

Typical examples are multilayer parisons of poly(ethylene) terephthalate and copolyester; poly(- 50 ethylene) terephthalate, nylon and copolyester; poly(ethylene) terephthalate, adhesive, nylon, glue and poly(ethylene) terephthalate.

The process is also applicable to blends of poly(ethylene) terephthalate with polymers which provide desirable barrier properties wherein the poly(ethylene) terephthalate comprises a major portion of the total weight, preferably at least 70% of the total weight.

Thus, as used herein in the specification and claims, the term poly(ethylene) terephthalate is intended to include the above poly(ethylene) terephthalate containing materials.

The following parameters produce satisfactory results for poly(ethylene) terephthalate:

1 GB2195287A 5 Orientation temperature - 1100c Heat setting temperature 250C Heat setting time 0.5 - 10 sec.

Cooling time 1.0 - 10 sec.

Mold open delay 0.5 - 9.5 sec.

A preferred range of parameters comprises a heat setting temperature which ranges between to 230'C, a heat setting time ranging between 1 and 5 seconds, mold open delay ranging 15 between 0.5 to 5 seconds, and cooling after mold opening ranging between 0.8 and 1.2 seconds.

The present invention has particular utility for making complex containers such as containers that are non-cylindrical, for example, oval in cross section, which may comprise two or more cylindrical portions of different cross sectional dimensions, and which incorporate combinations 20 of cylindrical portions, inclined portions, flutes, ribs and the like.

Referring to Figs. 5 and 6, for example, such containers 30 comprise eight vertical flutes 31, three horizontal frustoconical ribs 32, and a reverse frusto-concial shoulder portion 33.

In the following test results, the containers had the configuration shown in Figs. 5 and 6 and exhausting of blowing fluid and introduction of cooling were initiated simultaneously. The mold 25 opening delay time was measured from the beginning of the exhaust and introduction of cooling fluid. The bottom temperatures of the molds were lower in order that there would be less heat setting of the thicker bottom of the container.

In the following test results, the containers were made from poly(ethylene) terephthalate having an IN. of 0.80. The axial stretch ratio was 1.6X and hoop stretch ratio ranged from 4.8X to 30 5.3X in the area of flutes 31; ranged from 3.4X to 5.3X in the area of ribs 32; ranged from 3.4X to 3.66X in shoulder portion 33.

In connection with showing how the importance of positioning of the nozzle is in making complex containers, tests were conducted by making containers shown in Figs. 5 and 6 having a height of 9-1/2 inches and a satisfactory overflow container volume without shrinkage being 35 about 1490 cc.

The following TABLE A summarizes the results:

6 GB2195287A 6 TABLE A

Nozzle Location Bottle Number 1A 2A 3A 4A 5 Crystallization Temp, OC 224 224 224 224 Time, Sec. 6 6 6 6 10 1 Bottom Temp, OC. l2 122 122_ 122 Mold Open 15 Delay, Sec. 4 4 4 4 C02 On Time, Sec. 5 5 5 5 20 Nozzle Location, Distance From Bottom, Inch 2 21 3 31 Overflow 25 Vol., CC 1475.7 1481.0 1476.0 1478.5 It can be seen that when the nozzle location is between 2 and 3-1/2 inches from the bottom, 30 satisfactory containers with good definition and reduced post mold shrinkage (overflow volume) were obtained. Thus, it is necessary to construct and position the nozzle so that the cooling medium cools all portions of the containers.

TABLE B summarizes a series of tests of containers made with varying mold open delay and carbon dioxide cooling times.

7 GB2195287A 7 TABLE B

Bottle Number 1B. 2B 3B 4B Crystallization - 5 Temp, OC 228 228 228 228 Time, See. 5 5 5 5 Bottom Temp, "C 122 122 122 122 10 Mold Open Delay, Sec. 3 3 3 2 C02 On Time, 15 Sec. 4.2 3.8 3.5 2 Nozzle Locationt 20 Distance From Bottom, Inch 3 3 3 3 Overflow vol. ' cc 1509.6 1486.2 1477.2 1385.6 25 TABLE B (cont'd) 30 Bottle Number 5B 6B 7B 8B Crystallization 35 Temp, "C 228 228 228 228 Time, Sec. 5 5 5 5 Bottom Temp, OC 122 122 122 122 40 Mold Open Delay, Sec. 2 2 1.5 C02 On Time, 45 Sec. 3 2.8 2.5 2.5 Nozzle Location, Distance From Bottom, Inch 3 3 3 3 50 overflow Vol. ' CC 1476.4 1478.5 1436.1 1480.1 8 GB2195287A 8 TABLE B (cont'd) Bottle Number 9B 10B 11B 12B Crystallization Temp# 0C 228 228 228 228 Time, Sec. 5 5 5 5 Bottom Temp, OC 122 122 122 122 Mold Open Delay, Sec.- 1.5 1.5 1.0 1.0 C02 On Time, 15 Sec. 2.3 2.0 2.0 1.8 Nozzle Location, Distance From 20 Bottom, Inch 3 3 3 3 Overflow V01. 1 CC 1475.1 1445.6 1491.1 1476.3 25 TABLE B (contld) 30 Bottle Number 13B 14B 15B 16B Crystallization 35 Temp, "C 228 228 228 228 Time, Sec. 5 5 5 5 Bottom Temp, OC 122 122 122 122 40 Mold Open Delay, Sec. 1.0 0.8 0.8 0.8 C02 On Time, 45 Sec. 1.6 1.6 1.4 1.8 Nozzle Location, Distance From Bottom, Inch 3 3 3 3 50 1 Overflow vol., CC 1463.0 1473.2 1432.1 1490.4 9 GB2195287A It can be seen from TABLE B, bottle number 413, that where the mold opening delay and cooling times are the same, the resultant container is grossly collapsed. Moreover, where the difference between mold opening delay time and carbon dioxide application time is less than 0.5 second, collapsing or definition loss occurs, as shown in bottle numbers 4B, 713, 10B. In the case of bottle 15B, the combination of the mold opening delay and cooling times was not adequate to cool the container to the self-supporting condition. This can be remedied by decreasing the mold opening delay time, as shown in bottle number 11 B, compared with bottle number 10B, or bottle number 8B as compared to bottle number 7B. Alternatively, the cooling time can be increased as shown in bottle numbers 14B and 16B compared with bottle number 15B. The remaining containers were satisfactory within the definition of desired overflow volume 10 and general appearance.

TABLE C represents a series of tests wherein mold opening delay and CO, application time are the same at various heat setting or crystallization temperatures.

TABLE C 15

Bottle Number lc 2C 3C 4C Crystallization Temp, "C 149 149 149 177 Time, Sec. 2.5 2.5 2.5 2.5 20 Bottom Temp, OC 122 122 122 122 Mold Open 25 Delay, Sec. 2 3 4 2 C02 On Time, Sec. 2 3 4 2 Nozzle Location, 30 Distance From Bottom, Inch 3 3 3 3 Overflow 35 Vol.' CC 1366.3 1408.0 1408.0 1362.6 TABLE C (cont'd) 40 Bottle Number SC 6C 7C 8C 9C Crystallization 45 Temp, OC 177 177 205 205 205 Time, Sec. 2.5 2.5 2.5 2.5 2.5 Bottom Temp, OC 122 122 122 122 122 Mold Open 50 Delay, Sec. 3 4 2 3 4 C02 On Time, Sec. 3 4 2 3 4: 55 Nozzle Location, Distance From Bottom, Inch 3 3 3 3 3 Overflow 60 vol., cc 1391.9 1391.4 1340.9 1329.0 1355.2 All containers were grossly deformed and collapsed and were not acceptable.

It can be seen that in each instance the resultant container is grossly deformed and collapsed 65 GB2195287A 10 1^ and would not be acceptable commercially. Additional tests have shown that comparable containers with substantial loss of definition occurs at lower heat setting temperatures where the mold opening delay and cooling time are the same.

It can thus be seen that it is essential that the application of carbon dioxide be continued after 5 the mold has been opened in order to obtain satisfactory results.

The following TABLE D summarizes the properties obtained in typical examples of the container shown in Figs. 5 and 6:

TABLE D

PROPERTIES OF INTERNALLY COOLED CONTAINERS Heatset Temperature = 228C Heatset Time = 5 sec.

C02 Time = 5 sec.

MECHANICAL PROPERTIES AXIAL HOOP Elastic Modulus, kpsi _x 394 644 20 a 38 86 Yield Stress, kpsi x 14.9 27.3 25 a 0.5 0.9 Yield Strain, % x 6.3 6.0 a 0.2 --- 30 Ultimate Strength, kpsi x 16.9 46.5 a 1.2 4.1 3 UltimateElongation % x 51 19 cr 16 3 DENSITY Density at 25C, g/c.C. 1.3960 45 It can thus be seen that the mechanical properties and improved density are satisfactory.

When inherent viscosity is referred to herein, it is the viscosity as measured in a 60/40 weight ratio phenol /tetrachloroethane solution at 25'C. Density was determined by the method 50 described by ASTM 1505, entitled -Density Gradient Technique---.

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

The following TABLE E shows the onset-of-shrinkage results. It can be seen thatonset-of shrinkage is substantially increased by the method for making the container shown in Figs.

and 6 over the same container made without heat setting:

11 GB2195287A TABLE E

ONSET OF SHRINKAGE Heatset Temperature = 2280C Heatset Time = 5 sec.

C02 Time = 5 sec.

10 CONTAIIER ONSET OF SHRINKAGE, OC Heatset 11011C Non-Heatset 50"C 15 The onset-of-shrinkage temperature referred to herein was determined as described in Brady and Jabarin "Thermal Treatment of Cold-Formed Poly(Vinyl Chloride) Polymer Engineering and Science", pp. 686-90 of Vol. 17, No. 9, September 1977, except that the samples were cut 20 from the sidewalls of the bottles. No thermal treatment was effected on the cut samples prior to the tests.

TABLE F shows the results of tests conducted at lower heat setting time.

TABLE F 25

Bottle Number Crystallization Temp, OC 225 30 Time, Sec. 3 Bottom Temp, OC 132 Mold Open 35 Delay, Sec. 2.5 C02 On Time, Sec. 3.5 40 Nozzle Location, Distance From Bottom, Inch 31 overflow 45 Vol., CC 1490.0 It can be seen that satisfactory containers are obtained in accordance with the method at lower heat setting times. - It can be seen that there has been provided a method for making biaxially oriented heat set 50 containers having a high 6nset-of-shrinkage temperature.

In various tests of the heat setting method embodying the invention, it has been found that the resultant container can be readily cooled to substantially below 1OWC and can be handled easily and touched by operators per-forming the method.

Observations made in accordance with the well known light scattering test indicate that 55 containers made in accordance with the method appear to have more uniform crystalline size distribution in the body of the container than is obtained by prior known heat setting methods that require long periods of time to cool the container after heat setting. It is believed that this more uniform crystalline size distribution is due to rapid quenching or cooling achieved in accordance with the method.

The sequence of operation utilized in accordance with the method may be summarized as follows:

1. The parison is heated to the orientation temperature (90--100'C).

2. Parison is allowed to soak for a given period of time in order to equilibrate the inside and outside temperature.

12 GB2195287A 12 3. The parison is transferred to the blow station.

4. The mold is closed.

5. The parison is blown and heat set for a given period of time.

6. The container is exhausted.

7. While the container is exhausting, the liquid CO, is introduced.

8. The mold is opened and CO, injection is continuing.

9. C02 injection completed.

10. The container is unclamped and released.

In the case of containers having complex or free standing bottoms, a mold base is provided which remains in contact with the base of the container when the mold is opened and cooling 10 fluid continues to be applied to the interior of the container while the base mold is in engagement with the base of the container. The movable mold base can be applied also to a hemispherical bottom container to stabilize the container while the mold is open and cooling fluid is being applied.

Accordingly, it can be seen that there has been provided a method and apparatus for making partially crystalline, biaxially oriented heat set hollow plastic containers wherein the containers have reduced post mold shrinkage, increased density, increased onset-of-shrinkage temperature, satisfactory mechanical properties, which has a significantly lower cycle time; which permits heat set containers to be made that have complex configurations including oval containers; which involves low capital investment; which is easily to maintain; and which involves the use of lower 20 cost tooling; and which can be adapted readily to conventional machine for making biaxially oriented containers.

Claims

CLAIMS 25 1. A method for making a partially crystalline, biaxially

oriented heat set hollow plastic container from a hollow parison having an open end and a closed end comprising engaging the open end of a plastic parison which is at a temperature within its molecular orientation temperature range, enclosing the hot parison in a hot mold, the mold being at heat setting temperature, 30 expanding the plastic parison within the hot mold by internal pressurization to induce biaxial orientation of the plastic parison and force the plastic parison into intimate contact and conformance with the hot mold and to maintain contact by such internal pressurization between the mold and the biaxially oriented container for a time sufficient to induce partial crystallization in the biaxially oriented container, thereafter exhausting the blow molding fluid while continuously introducing a cooling fluid 35 which changes state when introduced into the mold such as liquid carbon dioxide into the biaxially oriented container and continuously exhausting cooling fluid from the container while the hot mold is closed for a period of time, opening the hot mold while continuing to introduce coolant fluid for a predetermined period of time until the container is cooled sufficiently to prevent significant shrinkage and finally releasing the container.
2. The method set forth in claim 1 wherein the step of introducing a cooling fluid is achieved by a nozzle positioned axially within the blown container and directing the cooling fluid radially and axially outwardly such that cooling fluid is introduced to substantially all areas of the interior surface of the container.
3. The method set forth in claim 1 or 2 wherein said plastic parison is made of poly(ethylene) terephthalate.
4. The method set forth in claim 3 wherein the heat setting temperature of the mold ranges between 120 and 250C.
5. The method set forth in claim 3 wherein the method is performed within the following 50 parameters:

Orientation temperature Heat setting temperature Heat setting time - 11VC - 250C Cooling time Mold open 'delay 0.5 - 10 sec.

1. 0 - 10 sec.

0.5 - 9.5 sec.
6. The method set forth in claim 5 wherein the heat setting temperature ranges between 180 to 230C, the heat setting time ranges between 1 and 5 seconds, the mold open delay ranges between 0.5 and 5 seconds, and the cooling after mold opening ranges between 0.8 and 1.2 65 4; 13 GB2195287A 1 seconds.
7. The method set forth in claim 6 wherein the heat setting temperature is about 225'C and the heat setting time is about 3 seconds.
8. The method set forth in claim 1 wherein said cooling fluid is selected from the group consisting of liquid carbon dioxide, liquid nitrogen or combined zero temperature air and water mist.
9. The method set forth in claim 1 wherein said cooling fluid comprises liquid carbon dioxide.
10. The method set forth in claim 1 wherein said mold includes a partible mold and a separate mold base about which the partible mold is closed including the step of maintaining engagement between the mold base and the container after the mold is open and while cooling 10 fluid is continuously introduced and continuously removed from said container while the mold is open.
11. The method set forth in claim 10 wherein said mold has a cavity defining a complex container.
12. The method set forth in claim 1 wherein said mold has a cavity defining a complex container.
13. A method for making a partially crystalline, biaxially oriented heat set hollow plastic container from a hollow parison having an open end and a closed end comprising engaging the open end of a poly(ethylene) terephthalate parison which is at a temperature within its molecular orientation temperature range ranging between 800C and 1 10'C, enclosing the hot parison in a hot mold, the mold being at heat setting temperature ranging between 1200C and 250'C, expanding the plastic parison within the hot mold by internal pressurization to induce biaxial orientation of the plastic parison and force the plastic parison into intimate contact and confor- mance with the hot mold and to maintain contact by such internal pressurization between the mold and the biaxially oriented container for a time ranging between 0.5 and 10 seconds sufficient to induce partial crystallization in the biaxially oriented container, thereafter exhausting the blow molding fluid while continuously introducing a cooling fluid which changes state when introduced into the mold such as liquid carbon dioxide into the biaxially oriented container and continuously exhausting cooling fluid from the container while the 30 hot mold is closed for a time ranging between 1 and 10 seconds, opening the hot mold after a time ranging between 0.5 and 9.5 seconds after introduction of cooling fluid is begun while continuing to introduce coolant fluid for a predetermined period of time until the container is cooled sufficiently to prevent significant shrinkage, and finally releasing the container.
14. The method set forth in claim 13 wherein the step of introducing a cooling fluid is achieved by a nozzle positioned axially within the blown container such that cooling fluid is introduced to substantially all areas of the interior surface of the container.
15. The method set forth in claim 13 wherein the heat setting temperature ranges between 180 to 230'C, the heat setting time ranges between 1 and 5 seconds, mold open delay ranging 40 between. 0.5 and 5 seconds, the cooling after mold opening ranges between 0.8 and 1.2 seconds.
16. The method set forth in claim 15 wherein the heat setting temperatuare is about 225'C and the heat setting time is about 3 seconds.
17. The method set forth in claim 13 wherein said cooling fluid is selected from the group 45 consisting of liquid carbon dioxide, liquid nitrogen or combined zero temperature air and water mist.
18. The method set forth in claim 13 wherein said cooling fluid comprises liquid carbon dioxide.
19. The method set -forth in claim 13 wherein said mold includes a partible mold and a 50 separate mold base about which the partible mold is closed including the step of maintaining engagement between the mold base and the container after the mold is open and while cooling fluid is continuously introduced and continuously removed from said container while the mold is open.
20. The method set forth in claim 19 wherein said mold has a cavity defining a complex container.
21. The method set forth in claim 13 wherein said mold has a cavity defining a complex container.
22. A method for making a partially crystalline, biaxially oriented heat set hollow plastic container from a hollow parison having an open end and a closed end comprising engaging the open end of a plastic parison which is at a temperature within its molecular orientation temperature range, enclosing the hot parison in a partible hot mold having a separate mold base which is separate from the partible mold, the mold being at heat setting temperature, expanding the plastic parison within the hot mold by internal pressurization to induce biaxial 65 14 GB2195287A 14 orientation of the plastic parison and force the plastic parison into intimate contact and conformance with the hot mold and to maintain contact by such internal pressurization between the mold and the biaxially oriented container for a time sufficient to induce partial crystallization in the biaxially oriented container, exhausting the blow molding fluid while continuously introducing a cooling fluid which changes state when introduced into the mold such as liquid carbon dioxide into the biaxially oriented container and continuously exhausting cooling fluid from the container while the hot mold is closed for a period of time opening the hot mold wile maintaining engagement of the mold base with the base of the container and while continuing to introduce coolant fluid for a predetermined period of time until 10 the container is cooled sufficiently to prevent significant shrinkage and finally releasing the container.
23. The method set forth in claim 22 wherein the step of introducing a cooling fluid is achieved by a nozzle positioned axially within the blown container such that cooling fluid is introduced to substantially all areas of the interior surface of the container.
24. The method set forth in claim 22 wherein said plastic parison is made of poly(ethylene) terephthalate.
25. The method set forth in claim 24 wherein the heat setting temperature of the mold ranges between 120 and 250'C.
26. The method set forth in claim 22 wherein the method is performed within the following 20 parameters:

Orientation temperature Heat setting temperature Heat setting time Cooling time Mold open delay - 110C - 25VC 0.5 - 10 sec.

1.0 - 10 sec.

0.5 - 9.5 sec.
27. The method set forth in claim 26 wherein the heat setting temperature ranges between to 230'C, the heat setting time ranges between 1 and 5 seconds, mold open delay ranging between 0.5 and 5 seconds, and the cooling after mold opening ranges between 0.8 and 1.2 35 seconds.
28. The method set forth in claim 27 wherein the heat setting temperature is about 225C and the heat setting time is about 3 seconds.
29. The method set forth in claim 22 wherein said cooling fluid is selected from the group consisting of liquid carbon dioxide, liquid nitrogen or combined zero temperature air and water 40 mist.
30. The method set forth in claim 22 wherein said cooling fluid comprises liquid carbon dioxide.
31. The method set forth in claim 22 wherein said mold includes a partible mold and a separate mold base about which the partible mold is closed including the step of maintaining engagement between the mold base and the container after the mold is open and while cooling fluid is continuously introduced and continuously removed from said container while the mold is open.
32. The method set forth in claim 31 wherein said mold has a cavity defining a complex container.
33. The method set forth in claim 22 wherein said mold has a cavity defining a complex container.
34. An apparatus for making a partially crystalline, biaxially oriented heat set hollow plastic container from a hollow parison having an open end and a closed end comprising means for engaging and disengaging the open end of a plastic parison which is at a tempera- 55 ture within its molecular orientation temperature range, a hot mold having mold sections which can be opened and closed enclosing the hot parison in said hot mold, the mold being at heat setting temperature, means for expanding the plastic parison within the hot mold by internal pressurization to induce biaxial orientation of the plastic parison and force the plastic parison into intimate contact 60 and conformance with the hot mold and to maintain contact by such internal pressurization between the mold and the biaxially oriented container for a time sufficient to induce partial crystallization -in the biaxially oriented container, means for thereafter exhausting the blow molding fluid while continuously introducing a cooling fluid which changes state when introduced into the mold such as liquid carbon dioxide into the 65 GB2195287A 15 biaxially oriented container and continuously exhausting cooling fluid from the container while the hot mold is closed for a period of time, means for continuing to introduce coolant fluid for a predetermined period of time after the mold is opened until the container is cooled sufficiently to prevent significant shrinkage.
35. The apparatus set forth in claim 34 wherein said means for introducing cooling fluid comprises a nozzle positionable axially within said container when the mold is closed and having aperture means for directing cooling fluid radially and axially outwardly toward substantially all areas of the interior surface of the container.
36. The apparatus set forth in claim 35 wherein said aperture means comprises at least one set of circumferentially spaced orifices for directing the cooling fluid radially and at least one set 10 of circumferentially spaced orifices for directing the cooling fluid axially and radially.
37. The apparatus set forth in claim 35 wherein said aperture means comprises a first set of circumferentially spaced apertures for directing cooling fluid radially toward the side wall of the container, a second set of circumferentially spaced orifices for directing the fluid radially and axially toward the open end of the container, and a third set of circumferentially spaced orifices 15 extending axially and radially toward the base of the container.
38. The apparatus set forth in claim 34 wherein said mold includes an axially movable base such that after the container is formed, the base may be maintained in engagement with the base of the container after the mold is opened.
39. The apparatus set forth in claim 38 wherein said mold has a cavity defining a complex 20 shape.
40. The apparatus set forth in claim 34 wherein said mold has a cavity defining a complex shape.
41. A method as claimed in claim 1, substantially as described.
42. Apparatus as claimed in claim 34, substantially as described with reference to the draw- 25 ings.

Published 1988 at The Patent Office, State House, 66/71 High Holborn, London WC 1 R 4TP. Further copies may be obtained from The Patent Office, Sales Branch, St Mary Cray, Orpington, Kent BF15 3RD. Printed by Burgess & Son (Abingdon) Ltd. Con. 1/87.