Thermal imaging methods in the blow molding process

Abstract

A method for thermally imaging a blow molding preform is provided that includes heating the preform, measuring the temperature around its longitudinal axis, and converting the temperature measurements into a two-dimensional thermal image.

Description

[Technical Field]

[0001] The present technology relates to a system and process capable of subjecting preforms to a blow molding process to produce multiple preforms having multiple temperature profiles. [Background technology]

[0002] This section provides background information related to the present disclosure that is not necessarily prior art.

[0003] Various products are distributed in plastic containers, such as containers formed from one or more polymers. Common polymers used to form containers include polyesters such as polyethylene terephthalate (PET), high- and low-density polyethylene (PE), polypropylene (PP), polycarbonate (PC), etc. Plastic containers can be manufactured using various blow molding processes, including injection blow molding, hydraulic blow molding, and extrusion blow molding, which can use a preform that is expanded with a fluid to form the resulting container.

[0004] Injection blow molding can be used to form certain plastic containers in one or more stages, which may include the use of a stretch rod. In a two-stage injection stretch blow molding process, a polymer can first be formed into a preform using an injection molding process. The preform can include the neck and finish of the resulting container (which may include threads thereon) and a closed distal end. The preform can then be heated above the glass transition temperature of the polymer, optionally stretched longitudinally with a stretch rod, and blown into a mold-fitting container using high-pressure gas (e.g., air). As the preform expands, it stretches and assumes the shape of the mold cavity. The polymer solidifies upon contact with the cold surface of the mold, and the finished hollow container is then ejected from the mold.

[0005] Hydraulic blow molding can form and fill a container in a single operation. A liquid product can be used to mold a polymer preform in a mold and fill the resulting container, with the liquid product then remaining in the finished container. A heated preform, much like a preform used in injection blow molding, can be placed in a mold, optionally stretched, and then rapidly inflated or filled to form a container using a liquid product instead of a gas. The combination of the molding and filling processes can thus optimize the packaging of liquid products by eliminating the time requirements for transporting empty containers and subsequent filling operations.

[0006] Various types of preforms can be used in such blow molding processes. Particular embodiments of preforms include injection-molded, rotationally symmetric preforms with an elongated, cylindrical side body, a rounded, closed bottom, and a neck with an upper opening. Other preforms are rotationally asymmetric, with thicknesses varying along the elongated axis to facilitate material distribution to form asymmetric containers. In either case, there may be an external thread finish section located adjacent to the opening, which may be delimited toward its bottom by a collar or the like. The thread finish section may be preserved during blow molding of the preform; this finish may form, for example, threads for a screw cap on a finished beverage container. In contrast, the remainder of the preform may be deformed or stretched during the blow molding process. The preform may be heated to a predetermined temperature to enable blow molding in a desired manner. Heating may be accomplished by various means, including infrared radiation using an infrared oven, effectively providing defined and / or uniform temperature control of the preform.

[0007] In particular, the polymer material of the preform (e.g., PET) can be such that the polymer strain-hardens as it is stretched. Therefore, the molding temperature during the blow molding process can be a determining factor for the resulting container. The strain-hardening effect can be taken into account in the production of PET containers for the purpose of controlling and optimizing the wall thickness distribution. Depending on the manufacturing process, heat can be applied by infrared radiation so that the preform is heated according to a temperature profile. In this way, warmer parts of the preform can deform preferentially over other parts, as long as necessary so that the resistance to stretching resulting from strain hardening is greater than, for example, the resistance of adjacent cooler parts. The temperature profile can be uniformly distributed around the periphery of the preform or can vary process-dependently along the preform's longitudinal axis. Multiple heating zones, for example, up to nine or more zones, can be used to apply a desired temperature profile to the preform. Different heating zones can be individually controlled, allowing the selected settings to remain constant over longer periods of heating device operation.

[0008] Preforms of different configurations may require different heating regimens or methods in preparation for blow molding into the resulting container. For example, preforms formed with or containing different sizes, shapes, thicknesses, different polymers or polymer combinations, layers, etc., can each have a predetermined temperature profile optimized for a particular blow molding process. A specific example includes different heating regimens to produce different temperature profiles for PET preforms versus PP preforms. Another example includes different heating regimens to produce the same temperature profile, although preforms may have different characteristics (e.g., preforms formed with the same material but with different thicknesses) that require different regimens to achieve the same temperature profile. Accordingly, various heating parameters can be tailored to a particular preform, including the number of heating zones, the temperature of a particular heating zone, the exposure time to a particular heating zone, etc.

[0009] Blow molding systems often include a preform heating means adjacent to the system, allowing the heated preform to be delivered to the mold and molded into the resulting container within a short time before the preform's desired temperature profile changes. For example, the preform's path of travel through an infrared oven can be adjusted to generate a predetermined temperature profile for a given preform. However, if the conditions of the blow molding system and / or process change, it may be necessary to modify the preform path or heating means to accommodate the new temperature profile for a given preform. Changing blow molding conditions may involve using a different preform type, changing the mold, changing blow molding parameters, etc. Therefore, it can be difficult to adapt a blow molding system and / or process to changing conditions that require a change in the preform temperature profile while maintaining continuous or high-throughput production of containers. To accommodate preforms with different properties, a blow molding system often needs to change one or more settings, reach one or more new equilibria, or adapt one or more physical parameters. Summary of the Invention [Problem to be solved by the invention]

[0010] Without proper temperature control, heated preforms may have improper material distribution and / or expansion during the blow molding operation, and the resulting containers may rupture (or "blow out") or fail cosmetic inspection. In refined gas blow molding processes, approximately 1,500 to 2,500 containers per million gas-blown containers are expected to suffer blowouts. Blowouts from liquid-blown containers are expected to be roughly the same. With liquid blow molding, blowouts result in leakage and waste of the liquid product filling the container, more than air leakage. When the blow molding liquid is water, blowouts may result in wasted water and minimal downtime for the blow molding equipment to dry. When the blow molding liquid is, for example, a petroleum product, pharmaceutical, or cosmetic, blowout can result in significant time due to cleaning procedures required to make the blow molding equipment usable again, and can result in wasted or unusable product, each of which alone may have a significant economic impact on the blow molding process and product cost, and the combination of these may make the liquid blow molding process for packaging products economically unviable. It would be desirable to develop a blow molding method that reduces the expected blowouts in a blow molding operation (liquid or gas) to about 25 blowouts per million containers molded.

[0011] In consideration of these issues, the present technology provides a method of thermally imaging preforms prior to a blow molding operation that minimizes blowouts and allows the resulting blow molding operation to be maintained at a continuous or high throughput. [Means for solving the problem]

[0012] Consistent with and consistent with the present invention, it has surprisingly been discovered how to thermally image a preform prior to the blow molding operation to minimize blowouts.

[0013] In one embodiment of the present invention, a method for creating a thermal image of a blow molding preform comprises the steps of providing a preform suitable for blow molding, heating the preform, measuring the temperature of at least a portion of the preform along a longitudinal axis of the preform and around its circumference, aggregating the measured temperatures of at least a portion of the preform, and converting the aggregated measured temperatures into a three-dimensional thermal image representative of the measured temperatures of at least a portion of the preform.

[0014] In another embodiment of the present invention, a method for producing a thermal image of a preform for blow molding comprises the steps of providing a preform suitable for blow molding, heating the preform, measuring the temperature of at least a portion of the preform along a longitudinal axis of the preform and around its circumference, aggregating the measured temperatures of at least a portion of the preform, converting the aggregated measured temperatures into a three-dimensional thermal image representative of the measured temperatures of at least a portion of the preform, and converting the three-dimensional thermal image into a two-dimensional thermal image representative of the measured temperatures of at least a portion of the preform.

[0015] In another embodiment of the present invention, a method for creating a thermal image of a blow molding preform comprises the steps of: providing a preform suitable for blow molding; heating the preform; providing an infrared camera; measuring the temperature of at least a portion of the preform along and around a longitudinal axis of the preform with the infrared camera; aggregating the measured temperatures of at least a portion of the preform; converting the aggregated temperatures into a graphical image representing the temperatures of at least a portion of the preform versus the measurement locations; converting the aggregated measured temperatures into a three-dimensional thermal image representing the measured temperatures of at least a portion of the preform; and converting the three-dimensional thermal image into a heat map representing the measured temperatures of at least a portion of the preform.

[0016] These and other advantages of the present invention will become readily apparent to those skilled in the art from the following detailed description of the preferred embodiments when considered in light of the accompanying drawings. [Brief explanation of the drawings]

[0017] [Figure 1] FIG. 1 is a plan view showing a schematic of an oven for heat treatment and thermal imaging of preforms. [Figure 2] 2 is a cross-sectional view including one of the heating means of FIG. 1 and a preform heated thereby. [Figure 3] 1 is an exemplary three-dimensional thermal image of a heated preform and the corresponding two-dimensional thermal image obtained therefrom. [Figure 4] Selective dissection of the images in Figure 3 is shown. [Figure 5] A side-by-side comparison of the two-dimensional thermal image of Figure 3 with a graphical representation of the thermal data used to generate the image. DETAILED DESCRIPTION OF THE INVENTION

[0018] The following description of the technology is merely exemplary in nature of the subject matter, manufacture, and use of one or more inventions and is not intended to limit the scope, application, or use of any particular invention claimed in this application, or in any other application that may claim priority to this application, or in any patent issued therefrom. With regard to the disclosed methods, the order of the steps presented is exemplary in nature; therefore, the order of the steps may be varied in various embodiments, including cases where certain steps may be performed simultaneously. As used herein, "A" and "an" indicate the presence of "at least one" of an element, and where possible, multiple instances of such elements may be present. Unless otherwise expressly stated, all numerical quantities herein are understood to be modified by the term "about," and in describing the broadest scope of the technology, all geometric and spatial descriptions are understood to be modified by the term "substantially." When applied to a numerical value, "about" indicates that the calculation or measurement allows for some imprecision in the value (with some approach to the precision of the value; approximately or reasonably close to the value; approximately). Instead, if for any reason the imprecision provided by "about" and / or "substantially" is not understood in the art in its ordinary sense, then "about" and / or "substantially" as used herein will indicate at least the variation that might result from ordinary methods of measuring or using such parameters.

[0019] All documents cited in this detailed description, including patents, patent applications, and scientific literature, are incorporated herein by reference unless expressly stated otherwise. In the event that a conflict or ambiguity may exist between a document incorporated by reference and this detailed description, the detailed description will control.

[0020] Although the open-ended term "comprising" is used herein to describe and claim embodiments of the present technology as synonymous with non-limiting terms such as including, containing, and having, embodiments can alternatively be described using more restrictive terms such as "consisting of" or "consisting essentially of." Thus, for any given embodiment reciting a material, component, or process step, the present technology also specifically includes embodiments consisting of, or consisting essentially of, such material, component, or process step, excluding (if consisting of), or excluding (if consisting essentially of), additional materials, components, or steps that affect a critical characteristic of the embodiment, even if such additional materials, components, or steps are not explicitly recited herein. For example, a description of a component or process reciting elements A, B, and C specifically contemplates embodiments consisting of, and consisting essentially of, A, B, and C, excluding element D, as may be described in the art, even if element D is not explicitly recited herein as excluded.

[0021] As referred to herein, the disclosure of ranges includes endpoints, unless otherwise specified, and includes all explicit values ​​and further divided ranges throughout the range. Thus, for example, a range "from A to B" or "from about A to about B" includes A and B. The disclosure of values ​​and ranges of values ​​for a particular parameter (amount, weight percent, etc.) does not exclude other values ​​and ranges of values ​​useful herein. It is contemplated that two or more specific exemplified values ​​for a given parameter may define the endpoints of a range of values ​​that can be claimed for that parameter. Similarly, the disclosure of two or more ranges of values ​​for a parameter (whether such ranges are nested, overlapping, or separate) is contemplated to encompass all possible combinations of the ranges of values ​​that can be claimed using the endpoints of the disclosed ranges. For example, if a parameter X is exemplified herein as having a value in the range of 1-10, or 2-9, or 3-8, it is also contemplated that parameter X may have other ranges of values, including 1-9, 1-8, 1-3, 1-2, 2-10, 2-8, 2-3, 3-10, 3-9, etc.

[0022] When an element or layer is referred to as "on," "engaged to," "connected to," or "coupled to" another element or layer, it can be directly on, engaged with, connected to, or coupled to the other element or layer, or intervening elements or layers can be present. In contrast, when an element is referred to as "directly on," "directly engaged to," "directly connected to," or "directly coupled to" another element or layer, there can be no intervening elements or layers. Other words used to describe relationships between elements should be interpreted similarly (e.g., "between" vs. "directly between," "adjacent" vs. "directly adjacent," etc.). As used herein, the term "and / or" includes any and all combinations of one or more of the associated listed elements.

[0023] Terms such as "first," "second," and "third" may be used herein to describe various elements, components, regions, layers, and / or sections; however, these elements, components, regions, layers, and / or sections should not be limited by these terms. These terms are used solely to distinguish one element, component, region, layer, or section from another region, layer, or section. As used herein, terms such as "first," "second," and other numerical terms do not imply a sequence or order unless clearly indicated by context. Thus, a first element, component, region, layer, or section described below could be referred to as a second element, component, region, layer, or section without departing from the teachings of the exemplary embodiments.

[0024] Spatially relative terms such as "inside," "outside," "below," "belower," "lower," "above," and "upper" may be used herein for ease of description to describe the relationship of one element or feature to another element(s) or feature(s), as shown in the figures. Spatially relative terms may be intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. For example, if the illustrated device were turned over, elements described as "below" or "below" the other element or feature would be oriented "above" the other element or feature. Thus, the illustrative term "below" can encompass both an orientation of above and below. The device may also be otherwise oriented (rotated 90 degrees or at other orientations), and the spatially relative descriptions used herein would be interpreted accordingly.

[0025] 1, the present technology is depicted in a method of thermal imaging using a heating system 10 and a method of thermally imaging a preform 12 and its temperature profile, and a method of using such a system, particularly in blow molding a container (not shown) from the preform 12. The system 10, which will be described in more detail herein, generally includes a camera 14 and a heating means 16.

[0026] With respect to the preform 12, FIG. 2 illustrates an exemplary preform 12 having a longitudinal axis O and an overall shape resembling a test tube. The preform 12 has a neck 18, a shoulder 20, a body 22, and a closed-off bottom 24. Typically, the neck 18 and shoulder 20 are each formed and in their final shape upon entry into the system 10 and do not need to be heated or thermally imaged as contemplated herein. Thus, typically, only the body 22 and bottom 24 are thermally treated and thermally imaged by the system 10, although the entire preform 12 may be heated if desired. The tubular body 22 of the preform 12 includes a neck 18 whose upper end is closed by a hemispherical bottom 24 and whose lower end is already in the defined shape of the neck 18 of the container, with a radially outwardly extending annular shoulder 20 that roughly defines the unheated portion of the preform 12 from its heated portion. Preforms 12 can be formed from polyester materials such as polyethylene terephthalate (PET) and other polyesters, polypropylene, acrylonitrile acid esters, vinyl chloride, polyolefins, polyamides, and derivatives, blends, and copolymers thereof. As shown, preforms 12 have a shape well known to those skilled in the art similar to a test tube, with a generally cylindrical cross-section and a length that is typically about 50% of the resulting container height; alternatively, preforms 12 may have any shape, length, and be formed from any material as desired. As described herein, the heat treatment performed in system 10 is intended to prepare preforms 12 for conversion by blowing with a gas or liquid to form each preform 12 into a container.

[0027] In system 10, each preform 12 is provided at the entrance of infeed station E via a magnetic levitation track, rail, or other transport mechanism (not shown). Preforms 12 are then individually loaded onto conveyor 26, which transports preforms 12 through system 10 and ultimately to exit S of system 10 for further processing steps 28, as described in more detail below. Further processing steps 28 may include transporting preforms 12 for re-entry into one of entrances E for additional heating, rejection, and recycling, or transporting preforms 12 to a blow mold loading station (not shown) for forming the preforms 12 into containers.

[0028] Each preform 12 enters the system 10 (which is at ambient temperature) placed on a spindle 30 (as shown in FIG. 2 ), which allows the preform 12 to rotate 360° as it passes through the system 10. Each preform 12 is transported through the system 10 by a conveyor 26 and passes through a series of heating means 16. The heating means 16 may be, for example, an infrared oven or any other suitable heating means known to those skilled in the blow molding arts. Direct and / or indirect (e.g., reflected) heat energy may be applied by the heating means 16. Multidirectional application of heat energy may be used, as may the preform 12 itself, which is moved, spun, or rotated relative to various heat radiation sources in the various heating means 16. While any number of heating means 16 may be utilized as desired, as shown in FIG. 1 , the system 10 includes three (3) heating means 16. As best shown in FIG. 2 , each heating means 16 includes five heating elements 32 to facilitate heating of each preform 12 at different heights of the preform 12 along its longitudinal axis O. It is understood that the number of heating means 16 and the heating elements 32 present in each heating means 16, or their operation during a given process, may vary based on the size or specifications of each preform 12, the material properties of each preform 12, etc. The heating means 16 are longitudinally spaced along the conveyor 26 through the system 10 to impart a desired thermal profile to the preform 12 that enables optimization of the distribution of plastic material during the remaining steps in the pre-stretching and blow molding process. The thermal profile may vary or define a gradient along the longitudinal axis O of each preform 12. Alternatively, the thermal profile may be constant across the length of the preform 12. Additionally, the thermal profile may vary across the thickness of the preform 12, for example, so that material on the outside of the preform 12 is at a higher temperature than material on the inside of the preform 12. The actual thermal profile will depend on the particular design of the preform 12, including its shape and material composition, material distribution, and the design of the resulting container that will be formed.As each preform 12 passes the heating means 16 , it is rotated on its spindle 30 so that it is heated by the heating means 16 until it reaches the camera 14 .

[0029] As shown in FIG. 1 , camera 14 is an infrared camera adapted to inspect and measure the temperature of each preform 12 along its longitudinal axis O and throughout its circumference. Camera 14 measures the temperature of preform 12 along axis O and the entire circumference of preform 12 at a predetermined and desired number of data points and / or at a desired resolution (constrained by camera 14). For example, data points correspond to the height of each of heating elements 32 and / or the portion of preform 12 between them, along each angle of the circumference of preform 12 and / or the area between them. Camera 14 is in electronic communication with a computer 34 or other data processor (not shown) that can process and / or compile the thermal property data measured by camera 14. For example, computer 34 converts the thermal property data of preform 12 into a three-dimensional thermal image 36 of each preform 12, as best shown in FIG. 3 . Computer 34 can then convert the three-dimensional thermal image 36 into a two-dimensional thermal image 38 (also known as a heat map). Alternatively, the computer 34 may convert the thermal property data directly into a two-dimensional thermal image 38. The image 38, viewed from left to right, is a representation of temperature measurements of the preform 12 from about 0° to about 359° taken as the preform 12 rotates on the spindle 30. In this manner, the temperature profile of the three-dimensional preform 12 can be viewed in two dimensions. Furthermore, the temperature profile of the preform 12 can be viewed overall or in desired regions along a longitudinal region 40, as shown, for example, in FIG. 4 . By way of example and best shown in FIG. 4 , the three-dimensional thermal image 36 can be divided into a desired number of longitudinal regions, such as 359 longitudinal regions corresponding to each angle of the preform 12 rotated about its axis O from about 0° to about 359°. In this manner, specific longitudinal regions 40 of the three-dimensional thermal image 36 and the preform 12 itself can be more easily and readily observed on the two-dimensional thermal image 38 without having to access and / or rotate the three-dimensional thermal image 36.

[0030] As described above, the temperature of the preform 12 is compiled by the computer 34. The measured temperatures are then plotted against the measurement location on the preform 12, as shown in graph 42 of Figure 5. As shown in graph 42, the temperature of the preform 12 at each temperature measurement (x-axis) taken by the camera 14 is plotted against the location of that measurement (x-axis) on the preform 12. In this way, graph 42, which is a numeric / graphical representation of the temperature measurements, can be easily compared and directly correlated with the two-dimensional thermal image 38, which is a color-based heat map.

[0031] By creating a two-dimensional thermal image 38, temperature measurements of the heated preform 12 can be easily and readily confirmed before the preform 12 is transferred to the blow molding station and formed into a final container. In some cases, the thermal images 36, 38 and / or graph 42 may indicate that the preform 12 has "cold areas" 44 or "warm areas" 46. Such areas 44, 46 may result in blowouts during blow molding and thus require remedial action during heating of the preform 12. The exact locations of such areas 44, 46 can be precisely located by observing and analyzing the thermal images 36, 38 and / or graph 42, so that remedial action can be taken to ensure proper heating of the preform 12 to minimize blowouts during blow molding into a container. Remedial action can include one or more adjustments to the processing parameters and settings of the system 10, including adjustments to the heating means 16 or particular heating elements 32 to increase or decrease the temperature of any portion of the preform 12 (e.g., regions 44, 46), as desired, so that subsequent preforms have different, acceptable temperature profiles to minimize blowouts during blow molding. Additional remedial action can be, for example, adjusting upward or downward the spin speed of the spindle 30 on which each preform 12 is placed, or increasing or decreasing the residence time of the preforms 12 in the system 10 (or the speed of the conveyor 26), and / or increasing or decreasing the cooling airflow within the system 10.

[0032] The exemplary embodiments are provided so that this disclosure will be thorough and will fully convey its scope to those skilled in the art. Numerous specific details are set forth, such as examples of specific components, devices, and methods, to provide a thorough understanding of the embodiments of the present disclosure. It will be apparent to those skilled in the art that specific details need not be employed, and that the exemplary embodiments may be embodied in many different forms, and neither should be construed to limit the scope of the present disclosure. In some exemplary embodiments, well-known processes, well-known device structures, and well-known techniques are not described in detail. Equivalent changes, modifications, and variations of some embodiments, materials, compositions, and methods can be made within the scope of the present technology with substantially similar results.

Claims

1. 1. A method for heating a blow molding preform, comprising: Providing a preform suitable for blow molding; heating the preform while conveying the preform through a heating system having at least one heating means; measuring the temperature of at least a portion of the preform along its longitudinal axis after transport through the at least one heating means of the heating system with a camera all around the preform, wherein the preform is rotated at least 360° around its longitudinal axis during said measuring step; aggregating the measured temperatures of the at least a portion of the preform; converting the collected measured temperatures into a three-dimensional thermal image representative of the measured temperatures of the at least a portion of the preform; performing a processing step based on analysis of the three-dimensional thermal image, when the analysis of the three-dimensional thermal image determines that the preform does not have an acceptable temperature profile, conveying the preform from the outlet of the heating system back to the inlet of the heating system for additional heating by the at least one heating means; or a step of conveying the preforms from an outlet of the heating system for recycling the preforms and rejecting the preforms unsuitable for blow molding.

2. 10. The method of claim 1, wherein in the converting step, the aggregated temperatures are converted into a two-dimensional thermal image representing a portion of the preform measured around the periphery of the preform along a longitudinal axis of the preform.

3. The method of claim 2 further comprising converting the three-dimensional thermal image into a two-dimensional thermal image.

4. The method of claim 3 , wherein the two-dimensional thermal image is a heat map.

5. The method of claim 4 , wherein during the heating step, the preform is rotated at least 360° about its longitudinal axis.

6. 6. The method of claim 5, wherein the heat map represents measurements of the circumference of the preform from about 0° to about 359° of the at least part of the preform.

7. The method of claim 6 , wherein said at least a portion of said preform is a body of said preform.

8. The method of claim 1 further comprising converting the aggregated temperatures into a graphical image representing the temperature of the at least a portion of the preform versus measurement location.

9. The method of claim 1 , wherein the camera is an infrared camera.

Images