WO2016048468A1 - Compositions and methods for manufacturing thermoformed containers - Google Patents

Compositions and methods for manufacturing thermoformed containers Download PDF

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Publication number
WO2016048468A1
WO2016048468A1 PCT/US2015/044836 US2015044836W WO2016048468A1 WO 2016048468 A1 WO2016048468 A1 WO 2016048468A1 US 2015044836 W US2015044836 W US 2015044836W WO 2016048468 A1 WO2016048468 A1 WO 2016048468A1
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WO
WIPO (PCT)
Prior art keywords
film
material sheet
container
amorphous polymers
thermoformed
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Application number
PCT/US2015/044836
Other languages
French (fr)
Inventor
Steve BOWEN
Vivek CHOUGULE
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Printpack Illinois, Inc.
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Printpack Illinois, Inc. filed Critical Printpack Illinois, Inc.
Publication of WO2016048468A1 publication Critical patent/WO2016048468A1/en

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Classifications

    • BPERFORMING OPERATIONS; TRANSPORTING
    • B29WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29CSHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
    • B29C51/00Shaping by thermoforming, i.e. shaping sheets or sheet like preforms after heating, e.g. shaping sheets in matched moulds or by deep-drawing; Apparatus therefor
    • B29C51/14Shaping by thermoforming, i.e. shaping sheets or sheet like preforms after heating, e.g. shaping sheets in matched moulds or by deep-drawing; Apparatus therefor using multilayered preforms or sheets
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B29WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29CSHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
    • B29C51/00Shaping by thermoforming, i.e. shaping sheets or sheet like preforms after heating, e.g. shaping sheets in matched moulds or by deep-drawing; Apparatus therefor
    • B29C51/08Deep drawing or matched-mould forming, i.e. using mechanical means only
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B29WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29CSHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
    • B29C51/00Shaping by thermoforming, i.e. shaping sheets or sheet like preforms after heating, e.g. shaping sheets in matched moulds or by deep-drawing; Apparatus therefor
    • B29C51/002Shaping by thermoforming, i.e. shaping sheets or sheet like preforms after heating, e.g. shaping sheets in matched moulds or by deep-drawing; Apparatus therefor characterised by the choice of material

Definitions

  • the present disclosure relates generally to container manufacturing, and more specifically to compositions and methods for manufacturing thermoformed containers.
  • thermoforming involves heating a material sheet to a temperature at which it is soft, draping or drawing the heated material sheet into a molded cavity by vacuum or pressure, and then cooling the material sheet to a temperature at which it can maintain its shape of a semi-rigid container. The container is then filled with product and a layer of film is used to seal the container.
  • This process can also include aseptic sterilization of the material sheet, aseptic sterilization of the container, as well as providing an aseptic environment for filling food product into the container.
  • thermoforming is a low-pressure and low-temperature process.
  • the material sheet that serves as feedstock to the thermoforming process comprises thermoplastic polymers.
  • Typical easy to form thermoplastic polymers used in thermoforming include amorphous polymers such as polystyrene and polyvinyl chloride.
  • these typical easy to form thermoplastic polymers that are used to form the material sheet have been found to have drawbacks due to limited functionality, for example higher temperature usage in microwave heating, hot filling of the product, and thermal sterilization.
  • thermoplastic materials such as polypropylene (“PP”) or blends of polypropylene and polyethylene (“PE”), are sometimes used to form the material sheet for thermoforming processes.
  • PP polypropylene
  • PE polyethylene
  • certain manufacturing and performance challenges are inherent to process these material sheets in thermoforming.
  • the processing window required to produce high quality containers of polyolefin material is very narrow.
  • the processing window is dictated by the ease of forming the container, as well as the material strength which contributes to its resistance to sagging.
  • the processing window is determined by balancing the ease of forming and resistance to sagging.
  • the resulting thermoformed containers may experience mechanical failure.
  • thermoformed containers Accordingly, there is a need for improved polyolefin-based compositions for material sheets used in thermoforming and methods for manufacturing thermoformed containers.
  • a material sheet for thermoforming which includes a film having an elongational viscosity of greater than about 20,000 Pa.s at 140 °C and a strain rate of about 4 s "1 .
  • the film comprises one or more thermoplastic polyolefins and one or more amorphous polymers.
  • a method for making a material sheet for thermoforming includes forming a film having an elongational viscosity of greater than about 20,000 Pa.s at 140 °C and a strain rate of about 4 s "1 .
  • the film comprises one or more thermoplastic polyolefins and one or more amorphous polymers.
  • thermoformed container which includes a container wall comprising a film having an elongational viscosity of greater than about 20,000 Pa.s at 140 °C and a strain rate of about 4 s "1 .
  • the film comprises one or more thermoplastic polyolefins and one or more amorphous polymers.
  • a method for making a thermoformed container includes providing a material sheet comprising a film, having an elongational viscosity of greater than about 20,000 Pa.s at 140 °C and a strain rate of about 4 s "1 , and comprises one or more thermoplastic polyolefins and one or more amorphous polymers; heating the material sheet; drawing the heated material sheet into a molded cavity to form a container; and cooling the container.
  • FIG. 1A is a cross-sectional plan view of a material sheet for manufacturing thermoformed containers in accordance with an embodiment of the present disclosure.
  • FIG. IB is a cross-sectional plan view of a material sheet for manufacturing thermoformed containers in accordance with an embodiment of the present disclosure.
  • FIG. 1C is a cross-sectional plan view of a material sheet for manufacturing thermoformed containers in accordance with an embodiment of the present disclosure.
  • FIG. 2A is a cross-sectional plan view of a material sheet for manufacturing thermoformed containers in accordance with an embodiment of the present disclosure.
  • FIG. 2B is a cross-sectional plan view of a material sheet for manufacturing thermoformed containers in accordance with an embodiment of the present disclosure.
  • FIG. 2C is a cross-sectional plan view of a material sheet for manufacturing thermoformed containers in accordance with an embodiment of the present disclosure.
  • FIG. 3 is a block diagram illustrating an embodiment of a method for making a thermoformed container.
  • FIG. 4 is a schematic diagram of exemplary embodiment of a thermoform fill seal process in accordance with the present disclosure.
  • the present invention addresses the above-described needs by providing improved polyolefin-based compositions and methods for manufacturing containers via a thermoforming process.
  • material sheet compositions, containers made therefrom, and methods for making these containers are described below.
  • the polyolefin-based compositions used to form material sheets for thermoforming processes should provide one or more of the following properties: (i) low thermal expansion and shrinkage (ii) good sagging resistance; (iii) ease of forming and broader thermoforming window. Accordingly, polyolefin-based compositions that can provide lower thermal expansion and shrinkage, higher sagging resistance, while also being easy to form and having a broader thermoforming window have been developed.
  • polyolefin-based compositions that provide lower thermal expansion and shrinkage, higher sagging resistance, while further having a broader thermoforming window, have been developed for the manufacture of thermoformed containers. That is, the material sheet compositions disclosed herein advantageously display an improved processing ability of polyolefins in thermoforming.
  • the thermoformed container includes a container wall formed from a material sheet comprising a film having an elongational viscosity of greater than about 20,000 Pa.s at 140 °C and a strain rate of about 4 s "1 .
  • the maximum elongational viscosity of the film is 2,000,000 Pa.s at 140 °C and a strain rate of about 4 s "1 .
  • the film comprises one or more thermoplastic polyolefins and one or more amorphous polymers.
  • the one or more thermoplastic polyolefins are polypropylenes ("PP"), polyethylenes (“PE”), or any combination thereof.
  • the one or more amorphous polymers may include one or more cyclic olefin copolymers ("COC"), polyamides, polyvinyl chlorides (“PVC”), polyetherimides, polyamideimides, polyarylates, or any combination thereof.
  • the film may be formed as a mono-layer film or multi-layer film by way of extrusion, lamination, or the like.
  • the film may include a mono-layer blend of COC and PP.
  • the film may include three layers in which the first layer may include COC and the second and third layers may each include PP, for example.
  • the one or more thermoplastic polyolefins present in the film are in an amount from about 50 to about 95 percent by weight of the film and the one or more amorphous polymers present in the film are in an amount from about 5 to about 50 percent by weight of the film.
  • the film may include the one or more thermoplastic polyolefins from about 60 to about 80 percent by weight of the film and the one or more amorphous polymers from about 20 to about 40 percent by weight of the film.
  • the film may include one or more thermoplastic polyolefins and one or more amorphous polymers in a weight ratio of 95:5, 90: 10, 85: 15, 80:20, 75:25, 70:30, 65:35, 60:40, 55:45, 50:50, 45:55, 40:60, 35:65, 30:70, 25:75, 20:80, 15:85, 10:90, 5:95, and ratios therebetween, depending on the desired container thermoforming processing.
  • the material sheet may also include additives to enhance the properties of the material sheet or to impart additional properties.
  • additives include process aids to assist in the extrusion process of the material sheet, slip additives to help prevent the material sheet from sticking to process machinery, oxygen scavengers, moisture scavengers, nucleators to increase setting time of polymer after thermoforming and to help minimize warpage, clarifiers to improve clarity, and antioxidants to improve thermal stability of polymers.
  • the material sheet may further include one or more barrier layers to extend the shelf life of food or beverage products to be packaged in a container made therefrom.
  • one or more barrier layers may be used where products to be packaged are sensitive to certain gases, or loss of volatiles, flavors, or aromas.
  • the one or more barrier layers may include ethylene vinyl alcohol, nylon, polyvinylidene chloride, liquid crystalline polymer, or any combination thereof.
  • the barrier layers may also include barrier enhancing additives, such as nano-additives or oxygen scavengers.
  • Embodiments of the material sheet may include a combination of either different or substantially similar one or more barrier layers. The location of the one or more barrier layers within the material sheet is determined based on, for example, the product to be packaged, to optimize the oxygen barrier performance and/or to minimize loss of flavors and aromas of such product.
  • the material sheet may also include one or more adhesive layers.
  • the adhesive layers may include PEgMA, PPgMA, EVA, EVAgMA, EMA, or any combination thereof. Similar or different one or more adhesive layers may be used in a single material sheet.
  • the adhesive layers may be disposed between the layer of the film and a barrier layer or between two barrier layers. Alternatively, in these instances, the layer of the film and/or the barrier layers may be disposed adjacent to one another without an adhesive layer therebetween.
  • the adhesive layers may be disposed between a layer of the film and a barrier layer, between two layers of the film, or between two barrier layers. Alternatively, in these instances, the layers of the film and/or the barrier layers, may be disposed adjacent to one another without an adhesive layer therebetween.
  • the material sheet of the present teachings may be extruded or laminated.
  • the film of the material sheet is an extruded mono-layer blend of one or more thermoplastic polyolefins and one or more amorphous polymers.
  • the film of the material sheet is either a coextruded or laminated multi-layer film in which at least one layer comprises one or more thermoplastic polyolefins and at least one layer comprises one or more amorphous polymers.
  • the material sheet forming the container wall may have a thickness from about 0.1 mm to about 3 mm.
  • the container wall has a thickness of less than about 1 mm.
  • multiple microlayers of material consisting of one or more amorphous polymers and one or more barrier polymers may be formed and included within the material sheet to enhance the thickness uniformity throughout the material sheet after thermoforming.
  • Exemplary embodiments of material sheets may include two outer layers and one or more intermediate layers disposed between the two outer layers, as illustrated in FIGS. 1A-1C and FIGS. 2A-2C.
  • at least one layer comprises one or more polyolefins and at least one other different layer comprises one or more amorphous polymers.
  • the first outer layer, 102a, 102b, 102c, 202a, 202b, 202c comprises one or more polyolefins or a blend of one or more polyolefins with one or more amorphous polymers and the second outer layer 106a, 106b, 106c, 206a, 206b, 206c, comprises one or more polyolefins or a blend of one or more polyolefin with one or more amorphous polymers.
  • an exemplary material sheet 100a includes the two outer layers 102a, 106a and one polymer layer 104a disposed between the two outer layers 102a, 106a.
  • the one polymer layer 104a comprises one or more polyolefins or a blend of one or more polyolefins with one or more amorphous polymers.
  • an exemplary material sheet 100b includes the two outer layers 102b, 106b and five intermediate layers disposed between the two outer layers 102b, 106b.
  • the five intermediate layers include two polymer layers 104b, 112b, one barrier layer 110b, and two adhesive layers 108b.
  • the first polymer layer 104b comprises one or more polyolefms or a blend of one or more polyolefms with one or more amorphous polymers and the second polymer layer 112b comprises one or more polyolefms or a blend of one or more polyolefms with one or more amorphous polymers.
  • the first adhesive layer 108b is in direct contact with the first polymer layer 104b and the barrier layer 110b, whereas the second adhesive layer 108b is in direct contact with the second polymer layer 112b and the barrier layer 110b.
  • an exemplary material sheet 100c includes the two outer layers 102c, 106c and thirteen intermediate layers disposed between the two outer layers 102b, 106.
  • the thirteen intermediate layers include four polymer layers 104c, 112c, three barrier layers 110c, and six adhesive layers 108c.
  • the three polymer layers 104c each comprise one or more polyolefms or a blend of one or more polyolefms with one or more amorphous polymers and the fourth polymer layer 112c comprises one or more polyolefms or a blend of one or more polyolefms with one or more amorphous polymers.
  • the adhesive layers 108c are disposed between the barrier layers 110c and polymer layers 104c, 112c.
  • an exemplary material sheet 200a includes the two outer layers 202a, 206a and one polymer layer 204a disposed between the two outer layer 202a, 106a.
  • the one polymer layer 204a comprises one or more amorphous polymers.
  • an exemplary material sheet 200b includes the two outer layers 202b, 206b and five intermediate layers disposed between the two outer layers 202b, 206b.
  • the five intermediate layers include two polymer layers 204b, 212b, one barrier layer 210b, and two adhesive layers 208b.
  • the first polymer layer 204b comprises one or more amorphous polymers and the second polymer layer 212b comprises one or more polyolefms or a blend of one or more polyolefms with one or more amorphous polymers.
  • the first adhesive layer 208b is in direct contact with the first polymer layer 204b and the barrier layer 210b, whereas the second adhesive layer 208b is in direct contact with the second polymer layer 212b and the barrier layer 210b.
  • an exemplary material sheet 200c includes the two outer layers 202c, 206c and thirteen intermediate layers disposed between the two outer layers 202c, 206c.
  • the thirteen intermediate layers include four polymer layers 204c, 212c, three barrier layers 210c, and six adhesive layers 208c.
  • the three polymer layers 204c each comprise one or more amorphous polymers and the fourth polymer layer 212c comprises one or more polyolefms or a blend of one or more polyolefms with one or more amorphous polymers.
  • the adhesive layers 208c are disposed between the barrier layers 210c and polymer layers 204c, 212c.
  • Thermoformed containers made with material sheets as discussed above display higher sagging resistance while being pliable and easy to form. Thus, these materials provide a broader processing window and display substantially uniform material distribution.
  • Thermoformed containers are generally produced by a two stage process, wherein the first stage a material sheet is produced and in the second stage, the material sheet is shaped (thermoforming stage).
  • the two stages may either directly follow each other (inline thermoforming) or they may not directly follow each other (off-line thermoforming), in which case the material sheet is stored first and only later fed to the thermoforming stage.
  • methods of making thermoformed containers include: (i) providing a material sheet comprising a film having an elongational viscosity of greater than about 20,000 Pa.s at 140 °C and a strain rate of about 4 s "1 , the film comprising one or more thermoplastic polyolefins and one or more amorphous polymers; (ii) heating the material sheet; (iii) drawing the heated material sheet into a molded cavity to form a container; and (iv) cooling the container.
  • the material sheet may be formed by way of extrusion, e.g. melt extrusion, lamination, or the like. Once formed, the material sheet is either directly fed or first stored as a roll and later roll fed into the thermoforming stage to form a thermoformed container. In either instance, as shown in FIG. 3, once the material sheet is provided 302, the thermoforming stage involves heating the material sheet 304, drawing the heated material sheet into a molded cavity 306, and then cooling the heated material sheet to form a container 308. In certain embodiments, the thermoforming stage may further include cutting/separating and releasing the cooled container from the molded cavity.
  • extrusion e.g. melt extrusion, lamination, or the like.
  • the thermoforming stage may be directly followed by filling the container with a product in-line, sealing the container, and trimming the container to separate the container from the remaining material sheet.
  • the thermoforming methods in accordance with the present disclosure may be employed in a thermoform-fill-seal type operation to manufacture a packaged product.
  • the containers are thermoformed from the material sheets of the present teachings, filled with product, and sealed in a continuous process.
  • a rollstock of material sheet 402 in accordance with the present disclosure is provided and fed into a heating oven 404.
  • the heated material sheet is then formed 406 into containers 408.
  • the thermoformed containers 408 are then filled 410 with product, sealed 412 and, when applicable, trimmed 414 to produce individual packaged products 416.
  • Various material sheets were produced using mono- or multi-layer co-extrusion processes. First, if required, the materials were dry blended in appropriate ratio and then fed to the respective extruder hoppers. Alternatively, if required, the materials can be wet blended by feeding multiple materials in appropriate proportion to an extruder and then the resulting melt, pallets, or powder is fed to the respective extruder hoppers. The extruder processing conditions such as temperature, and screw RPM were determined based on the polymer composition and desired structure. After extruding the sheet, sheet gauge and polish were achieved by controlling the roll stock parameters as the material sheet was cooled. Finally the material sheet was wound in a roll form.
  • the materials used to form the material sheets for thermoforming sample containers included: a mono-layer film of homopolymer PP, a mono-layer film of copolymer PP, a mono-layer film of LLDPE, a mono-layer film of COC, mono-layer film blends of PP and COC, mono-layer film blends of LLDPE and COC, and a multi-layer film of PP and COC.
  • Table 1 contains the material properties of the raw materials used throughout the examples.
  • a compatibilizer such as PPgMA or PEgMA was also included as a raw material.
  • Comparative container samples were made according to the foregoing methods, using various sheet materials.
  • Table 2 shows the performance observations of the thermoformed containers made using various sheet materials as indicated below.
  • the processing window, the sagging resistance, the material distribution, the top load strength, and the drop impact performance of the sample containers formed from the various material sheets were observed and recorded.
  • the test methods were qualitative based on observations.
  • the test methods including thickness at various locations on the container using precise Vernier Micrometer Thickness Gauge.
  • ASTM D2649-1 1 was used as a guideline.
  • ASTM D5420 was used as a guideline.
  • Copolymer PP Narrow processing window
  • Blends of PP and COC Broad processing window Blends of PP and COC Broad processing window.
  • Blends of LLDPE and COC Broad processing window Blends of LLDPE and COC Broad processing window.
  • Multi-layer film of PP and COC Broad processing window Multi-layer film of PP and COC Broad processing window.
  • the exemplary thermoformed containers formed using blends of PP and COC e.g., in a weight ratio of 90% PP: 10% COC to 60% PP:40% COC, and in one instance additionally 10% compatibilizer, or blends of LLDPE and COC, e.g., in a weight ratio of 90% PP: 10% COC to 60% PP:40% COC, or a multi-layer film of PP and COC, e.g., in a weight ratio in which a first layer of 100 % PP, a second layer of 75% PP:25% COC to 60% PP:40% COC, and a third layer of 100 % COC, displayed broad to very broad processing windows, excellent to good material distribution, and good to moderate sagging resistance.
  • Thermoformed containers made using a mono-layer film of only homopolymer PP, copolymer PP, or LLDPE displayed narrow to medium processing windows and poor to moderate material distribution. These results indicate that PP or PE by themselves may not produce acceptable thermoformed containers. However, the inventors found that combining amorphous polymers, such as for example COC, with polyolefins, such as for example PP or PE, either as a mono-layer or multilayer film, enhanced the performance and manufacturing properties of the material sheets and the thermoformed containers made therefrom.
  • amorphous polymers such as for example COC
  • polyolefins such as for example PP or PE
  • the term “substantially” is utilized herein to represent the inherent degree of uncertainty that may be attributed to any quantitative comparison, value, measurement, or other representation.
  • the term “substantially” is also utilized herein to represent the degree by which a quantitative representation may vary from a stated reference without resulting in a change in the basic function of the subject matter at issue.

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  • Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
  • Laminated Bodies (AREA)
  • Blow-Moulding Or Thermoforming Of Plastics Or The Like (AREA)
  • Containers Having Bodies Formed In One Piece (AREA)

Abstract

Material sheets and methods for making material sheets for thermoforming including a film having an elongational viscosity of greater than about 20,000 Pa.s at 140° C and a strain rate of about 4 s-1 is provided. The film includes one or more thermoplastic polyolefins and one or more amorphous polymers. Also provided are thermoformed containers and methods for making thermoformed containers including a container wall having a film with an elongational viscosity of greater than about 20,000 Pa.s at 140° C and a strain rate of about 4 s-1. The film includes one or more thermoplastic polyolefins and one or more amorphous polymers. A roll of film for forming a thermoformed container is also provided.

Description

COMPOSITIONS AND METHODS FOR MANUFACTURING
THERMOFORMED CONTAINERS
CROSS-REFERENCE TO RELATED APPLICATIONS This application claims priority to U.S. Provisional Application No. 62/054,170, filed September 23, 2014, which is incorporated by reference.
FIELD
The present disclosure relates generally to container manufacturing, and more specifically to compositions and methods for manufacturing thermoformed containers.
BACKGROUND
Various processes are utilized in converting polymer materials into containers that encapsulate many different products. Currently, the most widely used process to package products is thermo forming. In its most basic form, thermoforming involves heating a material sheet to a temperature at which it is soft, draping or drawing the heated material sheet into a molded cavity by vacuum or pressure, and then cooling the material sheet to a temperature at which it can maintain its shape of a semi-rigid container. The container is then filled with product and a layer of film is used to seal the container. This process can also include aseptic sterilization of the material sheet, aseptic sterilization of the container, as well as providing an aseptic environment for filling food product into the container. In contrast to other forming processes, such as for example injection molding or blow molding, thermoforming is a low-pressure and low-temperature process.
Generally, the material sheet that serves as feedstock to the thermoforming process comprises thermoplastic polymers. Typical easy to form thermoplastic polymers used in thermoforming include amorphous polymers such as polystyrene and polyvinyl chloride. However, these typical easy to form thermoplastic polymers that are used to form the material sheet have been found to have drawbacks due to limited functionality, for example higher temperature usage in microwave heating, hot filling of the product, and thermal sterilization. In addition, there is a desire for improved shelf life food packaging that contain these types of typical thermoplastic amorphous polymers.
As an alternative to these typical easy to form thermoplastic materials, traditional polyolefin materials, such as polypropylene ("PP") or blends of polypropylene and polyethylene ("PE"), are sometimes used to form the material sheet for thermoforming processes. However, it was found that certain manufacturing and performance challenges are inherent to process these material sheets in thermoforming. First, the thermal expansion and shrinkage of the material sheet that occur during the thermoform process causes significant alignment issues on standard thermoforming machines and high material wastage during startup. Second, after heating the material sheet, the material tends to stretch across the width under its own weight, which is referred to herein as "sagging." This sagging may cause a localized thinning of the material sheet, which will produce a container that has a non-uniform thickness. Third, the processing window required to produce high quality containers of polyolefin material is very narrow. The processing window is dictated by the ease of forming the container, as well as the material strength which contributes to its resistance to sagging. Thus, the processing window is determined by balancing the ease of forming and resistance to sagging. Moreover, the resulting thermoformed containers may experience mechanical failure.
Accordingly, there is a need for improved polyolefin-based compositions for material sheets used in thermoforming and methods for manufacturing thermoformed containers.
SUMMARY
In one aspect, a material sheet for thermoforming is provided which includes a film having an elongational viscosity of greater than about 20,000 Pa.s at 140 °C and a strain rate of about 4 s"1. The film comprises one or more thermoplastic polyolefins and one or more amorphous polymers.
In another aspect, a method for making a material sheet for thermoforming is provided. The method includes forming a film having an elongational viscosity of greater than about 20,000 Pa.s at 140 °C and a strain rate of about 4 s"1. The film comprises one or more thermoplastic polyolefins and one or more amorphous polymers.
In still another aspect, a thermoformed container is provided which includes a container wall comprising a film having an elongational viscosity of greater than about 20,000 Pa.s at 140 °C and a strain rate of about 4 s"1. The film comprises one or more thermoplastic polyolefins and one or more amorphous polymers.
In yet another aspect, a method for making a thermoformed container is provided. The method includes providing a material sheet comprising a film, having an elongational viscosity of greater than about 20,000 Pa.s at 140 °C and a strain rate of about 4 s"1, and comprises one or more thermoplastic polyolefins and one or more amorphous polymers; heating the material sheet; drawing the heated material sheet into a molded cavity to form a container; and cooling the container.
BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1A is a cross-sectional plan view of a material sheet for manufacturing thermoformed containers in accordance with an embodiment of the present disclosure.
FIG. IB is a cross-sectional plan view of a material sheet for manufacturing thermoformed containers in accordance with an embodiment of the present disclosure.
FIG. 1C is a cross-sectional plan view of a material sheet for manufacturing thermoformed containers in accordance with an embodiment of the present disclosure.
FIG. 2A is a cross-sectional plan view of a material sheet for manufacturing thermoformed containers in accordance with an embodiment of the present disclosure.
FIG. 2B is a cross-sectional plan view of a material sheet for manufacturing thermoformed containers in accordance with an embodiment of the present disclosure.
FIG. 2C is a cross-sectional plan view of a material sheet for manufacturing thermoformed containers in accordance with an embodiment of the present disclosure.
FIG. 3 is a block diagram illustrating an embodiment of a method for making a thermoformed container.
FIG. 4 is a schematic diagram of exemplary embodiment of a thermoform fill seal process in accordance with the present disclosure.
DETAILED DESCRIPTION
The present invention addresses the above-described needs by providing improved polyolefin-based compositions and methods for manufacturing containers via a thermoforming process. Several embodiments of material sheet compositions, containers made therefrom, and methods for making these containers are described below.
Parameters of different steps, components, and features of the embodiments are described separately, but may be combined consistently with this description and claims to enable still other embodiments as will be understood by those skilled in the art. To overcome the aforementioned challenges, the inventors have found that the polyolefin-based compositions used to form material sheets for thermoforming processes should provide one or more of the following properties: (i) low thermal expansion and shrinkage (ii) good sagging resistance; (iii) ease of forming and broader thermoforming window. Accordingly, polyolefin-based compositions that can provide lower thermal expansion and shrinkage, higher sagging resistance, while also being easy to form and having a broader thermoforming window have been developed.
Thermoformed Containers and Material Sheet Compositions
In certain embodiments, polyolefin-based compositions that provide lower thermal expansion and shrinkage, higher sagging resistance, while further having a broader thermoforming window, have been developed for the manufacture of thermoformed containers. That is, the material sheet compositions disclosed herein advantageously display an improved processing ability of polyolefins in thermoforming.
In certain embodiments, the thermoformed container includes a container wall formed from a material sheet comprising a film having an elongational viscosity of greater than about 20,000 Pa.s at 140 °C and a strain rate of about 4 s"1. In embodiments, the maximum elongational viscosity of the film is 2,000,000 Pa.s at 140 °C and a strain rate of about 4 s"1. In certain embodiments the film comprises one or more thermoplastic polyolefins and one or more amorphous polymers. In one embodiment, the one or more thermoplastic polyolefins are polypropylenes ("PP"), polyethylenes ("PE"), or any combination thereof. In another embodiment, the one or more amorphous polymers may include one or more cyclic olefin copolymers ("COC"), polyamides, polyvinyl chlorides ("PVC"), polyetherimides, polyamideimides, polyarylates, or any combination thereof. The film may be formed as a mono-layer film or multi-layer film by way of extrusion, lamination, or the like. In certain embodiments, the film may include a mono-layer blend of COC and PP. In an alternative embodiment, the film may include three layers in which the first layer may include COC and the second and third layers may each include PP, for example.
In one embodiment, the one or more thermoplastic polyolefins present in the film are in an amount from about 50 to about 95 percent by weight of the film and the one or more amorphous polymers present in the film are in an amount from about 5 to about 50 percent by weight of the film. For example, the film may include the one or more thermoplastic polyolefins from about 60 to about 80 percent by weight of the film and the one or more amorphous polymers from about 20 to about 40 percent by weight of the film. For example, the film may include one or more thermoplastic polyolefins and one or more amorphous polymers in a weight ratio of 95:5, 90: 10, 85: 15, 80:20, 75:25, 70:30, 65:35, 60:40, 55:45, 50:50, 45:55, 40:60, 35:65, 30:70, 25:75, 20:80, 15:85, 10:90, 5:95, and ratios therebetween, depending on the desired container thermoforming processing.
In certain embodiments, the material sheet may also include additives to enhance the properties of the material sheet or to impart additional properties. Non-limiting examples include process aids to assist in the extrusion process of the material sheet, slip additives to help prevent the material sheet from sticking to process machinery, oxygen scavengers, moisture scavengers, nucleators to increase setting time of polymer after thermoforming and to help minimize warpage, clarifiers to improve clarity, and antioxidants to improve thermal stability of polymers.
In instances where a high barrier thermoformed container is desired, the material sheet may further include one or more barrier layers to extend the shelf life of food or beverage products to be packaged in a container made therefrom. For example, one or more barrier layers may be used where products to be packaged are sensitive to certain gases, or loss of volatiles, flavors, or aromas. For example, the one or more barrier layers may include ethylene vinyl alcohol, nylon, polyvinylidene chloride, liquid crystalline polymer, or any combination thereof. The barrier layers may also include barrier enhancing additives, such as nano-additives or oxygen scavengers. Embodiments of the material sheet may include a combination of either different or substantially similar one or more barrier layers. The location of the one or more barrier layers within the material sheet is determined based on, for example, the product to be packaged, to optimize the oxygen barrier performance and/or to minimize loss of flavors and aromas of such product.
In certain embodiments, the material sheet may also include one or more adhesive layers. For example, in certain embodiments, the adhesive layers may include PEgMA, PPgMA, EVA, EVAgMA, EMA, or any combination thereof. Similar or different one or more adhesive layers may be used in a single material sheet. In instances where the film of the material sheet is mono-layered, the adhesive layers may be disposed between the layer of the film and a barrier layer or between two barrier layers. Alternatively, in these instances, the layer of the film and/or the barrier layers may be disposed adjacent to one another without an adhesive layer therebetween. In instances where the film of the material sheet is multi-layered, the adhesive layers may be disposed between a layer of the film and a barrier layer, between two layers of the film, or between two barrier layers. Alternatively, in these instances, the layers of the film and/or the barrier layers, may be disposed adjacent to one another without an adhesive layer therebetween.
The material sheet of the present teachings may be extruded or laminated. For example, in one embodiment, the film of the material sheet is an extruded mono-layer blend of one or more thermoplastic polyolefins and one or more amorphous polymers. In another embodiment, the film of the material sheet is either a coextruded or laminated multi-layer film in which at least one layer comprises one or more thermoplastic polyolefins and at least one layer comprises one or more amorphous polymers. In certain embodiments, the material sheet forming the container wall may have a thickness from about 0.1 mm to about 3 mm. In one embodiment, the container wall has a thickness of less than about 1 mm. In certain embodiments, multiple microlayers of material consisting of one or more amorphous polymers and one or more barrier polymers may be formed and included within the material sheet to enhance the thickness uniformity throughout the material sheet after thermoforming.
Exemplary embodiments of material sheets may include two outer layers and one or more intermediate layers disposed between the two outer layers, as illustrated in FIGS. 1A-1C and FIGS. 2A-2C. In each exemplary embodiment described below, at least one layer comprises one or more polyolefins and at least one other different layer comprises one or more amorphous polymers. In each exemplary embodiment, the first outer layer, 102a, 102b, 102c, 202a, 202b, 202c, comprises one or more polyolefins or a blend of one or more polyolefins with one or more amorphous polymers and the second outer layer 106a, 106b, 106c, 206a, 206b, 206c, comprises one or more polyolefins or a blend of one or more polyolefin with one or more amorphous polymers.
As shown in FIG. 1A, an exemplary material sheet 100a includes the two outer layers 102a, 106a and one polymer layer 104a disposed between the two outer layers 102a, 106a. The one polymer layer 104a comprises one or more polyolefins or a blend of one or more polyolefins with one or more amorphous polymers. As shown in FIG. IB, an exemplary material sheet 100b includes the two outer layers 102b, 106b and five intermediate layers disposed between the two outer layers 102b, 106b. The five intermediate layers include two polymer layers 104b, 112b, one barrier layer 110b, and two adhesive layers 108b. The first polymer layer 104b comprises one or more polyolefms or a blend of one or more polyolefms with one or more amorphous polymers and the second polymer layer 112b comprises one or more polyolefms or a blend of one or more polyolefms with one or more amorphous polymers. The first adhesive layer 108b is in direct contact with the first polymer layer 104b and the barrier layer 110b, whereas the second adhesive layer 108b is in direct contact with the second polymer layer 112b and the barrier layer 110b. As shown in FIG. 1C, an exemplary material sheet 100c includes the two outer layers 102c, 106c and thirteen intermediate layers disposed between the two outer layers 102b, 106. The thirteen intermediate layers include four polymer layers 104c, 112c, three barrier layers 110c, and six adhesive layers 108c. The three polymer layers 104c each comprise one or more polyolefms or a blend of one or more polyolefms with one or more amorphous polymers and the fourth polymer layer 112c comprises one or more polyolefms or a blend of one or more polyolefms with one or more amorphous polymers. The adhesive layers 108c are disposed between the barrier layers 110c and polymer layers 104c, 112c.
As shown in FIG. 2A, an exemplary material sheet 200a includes the two outer layers 202a, 206a and one polymer layer 204a disposed between the two outer layer 202a, 106a. The one polymer layer 204a comprises one or more amorphous polymers. As shown in FIG. 2B, an exemplary material sheet 200b includes the two outer layers 202b, 206b and five intermediate layers disposed between the two outer layers 202b, 206b. The five intermediate layers include two polymer layers 204b, 212b, one barrier layer 210b, and two adhesive layers 208b. The first polymer layer 204b comprises one or more amorphous polymers and the second polymer layer 212b comprises one or more polyolefms or a blend of one or more polyolefms with one or more amorphous polymers. The first adhesive layer 208b is in direct contact with the first polymer layer 204b and the barrier layer 210b, whereas the second adhesive layer 208b is in direct contact with the second polymer layer 212b and the barrier layer 210b. As shown in FIG. 2C, an exemplary material sheet 200c includes the two outer layers 202c, 206c and thirteen intermediate layers disposed between the two outer layers 202c, 206c. The thirteen intermediate layers include four polymer layers 204c, 212c, three barrier layers 210c, and six adhesive layers 208c. The three polymer layers 204c each comprise one or more amorphous polymers and the fourth polymer layer 212c comprises one or more polyolefms or a blend of one or more polyolefms with one or more amorphous polymers. The adhesive layers 208c are disposed between the barrier layers 210c and polymer layers 204c, 212c.
Thermoformed containers made with material sheets as discussed above display higher sagging resistance while being pliable and easy to form. Thus, these materials provide a broader processing window and display substantially uniform material distribution.
Methods of Making Thermoformed Containers
Thermoformed containers are generally produced by a two stage process, wherein the first stage a material sheet is produced and in the second stage, the material sheet is shaped (thermoforming stage). The two stages may either directly follow each other (inline thermoforming) or they may not directly follow each other (off-line thermoforming), in which case the material sheet is stored first and only later fed to the thermoforming stage.
In certain embodiments, methods of making thermoformed containers include: (i) providing a material sheet comprising a film having an elongational viscosity of greater than about 20,000 Pa.s at 140 °C and a strain rate of about 4 s"1, the film comprising one or more thermoplastic polyolefins and one or more amorphous polymers; (ii) heating the material sheet; (iii) drawing the heated material sheet into a molded cavity to form a container; and (iv) cooling the container.
The material sheet may be formed by way of extrusion, e.g. melt extrusion, lamination, or the like. Once formed, the material sheet is either directly fed or first stored as a roll and later roll fed into the thermoforming stage to form a thermoformed container. In either instance, as shown in FIG. 3, once the material sheet is provided 302, the thermoforming stage involves heating the material sheet 304, drawing the heated material sheet into a molded cavity 306, and then cooling the heated material sheet to form a container 308. In certain embodiments, the thermoforming stage may further include cutting/separating and releasing the cooled container from the molded cavity.
In certain embodiments, the thermoforming stage may be directly followed by filling the container with a product in-line, sealing the container, and trimming the container to separate the container from the remaining material sheet. Thus, the thermoforming methods in accordance with the present disclosure may be employed in a thermoform-fill-seal type operation to manufacture a packaged product. For example, as illustrated in FIG. 4, the containers are thermoformed from the material sheets of the present teachings, filled with product, and sealed in a continuous process. In FIG.4, a rollstock of material sheet 402 in accordance with the present disclosure is provided and fed into a heating oven 404. The heated material sheet is then formed 406 into containers 408. The thermoformed containers 408 are then filled 410 with product, sealed 412 and, when applicable, trimmed 414 to produce individual packaged products 416.
The present teachings may be further understood with reference to the following non-limiting examples.
Examples
Various material sheets were produced using mono- or multi-layer co-extrusion processes. First, if required, the materials were dry blended in appropriate ratio and then fed to the respective extruder hoppers. Alternatively, if required, the materials can be wet blended by feeding multiple materials in appropriate proportion to an extruder and then the resulting melt, pallets, or powder is fed to the respective extruder hoppers. The extruder processing conditions such as temperature, and screw RPM were determined based on the polymer composition and desired structure. After extruding the sheet, sheet gauge and polish were achieved by controlling the roll stock parameters as the material sheet was cooled. Finally the material sheet was wound in a roll form.
The materials used to form the material sheets for thermoforming sample containers included: a mono-layer film of homopolymer PP, a mono-layer film of copolymer PP, a mono-layer film of LLDPE, a mono-layer film of COC, mono-layer film blends of PP and COC, mono-layer film blends of LLDPE and COC, and a multi-layer film of PP and COC. Table 1 contains the material properties of the raw materials used throughout the examples. In some instances, a compatibilizer, such as PPgMA or PEgMA was also included as a raw material.
Figure imgf000011_0001
Comparative container samples were made according to the foregoing methods, using various sheet materials. Table 2 shows the performance observations of the thermoformed containers made using various sheet materials as indicated below.
Specifically, the processing window, the sagging resistance, the material distribution, the top load strength, and the drop impact performance of the sample containers formed from the various material sheets were observed and recorded. For the processing window and sagging resistance, the test methods were qualitative based on observations. For the material distribution, the test methods including thickness at various locations on the container using precise Vernier Micrometer Thickness Gauge. For the top load strength test method, ASTM D2649-1 1 was used as a guideline. For the drop impact performance test method, ASTM D5420 was used as a guideline.
Material Sheets Performance Observations
Homopolymer PP Narrow processing window.
Moderate sagging resistance.
Poor material distribution.
Copolymer PP Narrow processing window.
Poor sagging resistance.
Poor material distribution.
Too soft and low top load strength.
LLDPE Medium processing window.
Moderate sagging resistance.
Moderate material distribution.
Very soft and very low top load
strength.
COC Very broad processing window.
Good sagging resistance.
Excellent material distribution
Excellent top load strength.
Blends of PP and COC Broad processing window.
Moderate sagging resistance.
Good material distribution.
Good top load strength.
Medium drop impact performance.
Blends of LLDPE and COC Broad processing window.
Moderate sagging resistance.
Good material distribution.
Poor top load strength.
Multi-layer film of PP and COC Broad processing window.
Good sagging resistance.
Very good material distribution.
Good top load strength.
Table 2: Performance Observations of Containers Made Using
Various Material Sheet Materials
As can be seen from Table 2, the exemplary thermoformed containers formed using blends of PP and COC, e.g., in a weight ratio of 90% PP: 10% COC to 60% PP:40% COC, and in one instance additionally 10% compatibilizer, or blends of LLDPE and COC, e.g., in a weight ratio of 90% PP: 10% COC to 60% PP:40% COC, or a multi-layer film of PP and COC, e.g., in a weight ratio in which a first layer of 100 % PP, a second layer of 75% PP:25% COC to 60% PP:40% COC, and a third layer of 100 % COC, displayed broad to very broad processing windows, excellent to good material distribution, and good to moderate sagging resistance. Thermoformed containers made using a mono-layer film of only homopolymer PP, copolymer PP, or LLDPE displayed narrow to medium processing windows and poor to moderate material distribution. These results indicate that PP or PE by themselves may not produce acceptable thermoformed containers. However, the inventors found that combining amorphous polymers, such as for example COC, with polyolefins, such as for example PP or PE, either as a mono-layer or multilayer film, enhanced the performance and manufacturing properties of the material sheets and the thermoformed containers made therefrom.
For the purposes of describing and defining the present teachings, it is noted that the term "substantially" is utilized herein to represent the inherent degree of uncertainty that may be attributed to any quantitative comparison, value, measurement, or other representation. The term "substantially" is also utilized herein to represent the degree by which a quantitative representation may vary from a stated reference without resulting in a change in the basic function of the subject matter at issue.
It will be appreciated that various above-disclosed and other features and functions, or alternatives thereof, may be desirably combined into many other different products or applications. Various presently unforeseen or unanticipated alternatives, modifications, variations, or improvements therein may be subsequently made by those skilled in the art which are also intended to be encompassed by the following claims.

Claims

We claim:
1. A material sheet for thermoforming, said material sheet comprising:
a film comprising one or more thermoplastic polyolefins and one or more amorphous polymers, the film having
an elongational viscosity of greater than about 20,000 Pa.s at 140 °C and a strain rate of about 4 s 1.
2. The material sheet of claim 1, wherein the one or more polyolefins are selected from the group consisting of polypropylenes, polyethylenes, and any combinations thereof.
3. The material sheet of claim 1 , wherein the one or more amorphous polymers are one or more cyclic olefin copolymers, polyamides, polyvinyl chlorides, polyetherimides, polyamideimides, polyarylates, or any combination thereof.
4. The material sheet of claim 1, wherein the film is a mono-layer film.
5. The material sheet of claim 1, wherein the film is a multi-layer film.
6. The material sheet of claim 1, further comprising one or more barrier layers.
7. The material sheet of claim 1, further comprising one or more adhesive layers.
8. The material sheet of claim 1, further comprising one or more additives.
9. The material sheet of claim 1, wherein the one or more thermoplastic polyolefins are present in the film in an amount from about 50 to about 95 percent by weight of the film.
10. The material sheet of claim 1, wherein the one or more amorphous polymers are present in the film in an amount from about 5 to about 50 percent by weight of the film.
11. A method for making a material sheet for thermoforming, said method comprising: forming a film comprising one or more thermoplastic polyolefins and one or more amorphous polymers, the film having
an elongational viscosity of greater than about 20,000 Pa.s at 140 °C and a strain rate of about 4 s"1.
12. A thermoformed container, said container comprising:
a container wall comprising a film comprising one or more thermoplastic polyolefins and one or more amorphous polymers, the film having
an elongational viscosity of greater than about 20,000 Pa.s at 140 °C and a strain rate of about 4 s"1.
13. The thermoformed container of claim 12, wherein said container wall has a
thickness from about 0.1 mm to about 3.0 mm.
14. The thermoformed container of claim 12, further comprising a product therein.
15. The thermoformed container of claim 12, wherein the one or more thermoplastic polyolefins are selected from the group consisting of polypropylenes,
polyethylenes, and any combinations thereof.
16. The thermoformed container of claim 12, wherein the one or more amorphous polymers are one or more cyclic olefin copolymers, polyamides, polyvinyl chlorides, polyetherimides, polyamideimides, polyarylates, or any combination thereof.
17. The thermoformed container of claim 12, wherein the film is a mono-layer film.
18. The thermoformed container of clam 12, wherein the film is a multi-layer film.
19. The thermoformed container of claim 12, wherein the container wall further
comprises one or more barrier layers.
20. The thermoformed container of claim 12, wherein the container wall further comprises one or more adhesive layers.
21. The thermoformed container of claim 12, wherein the container wall further
comprises one or more additives.
22. The thermoformed container of claim 12, wherein the one or more thermoplastic polyolefins are present in the film in an amount from about 50 to about 95 percent by weight of the film.
23. The thermoformed container of claim 12, wherein the one or more amorphous polymers are present in the film in an amount from about 5 to about 50 percent by weight of the film.
24. A method for making a thermoformed container, said method comprising:
providing a material sheet comprising a film having an elongational viscosity of greater than about 20,000 Pa.s at 140 °C and a strain rate of about 4 s"1, the film comprising one or more thermoplastic polyolefins and one or more amorphous polymers;
heating the material sheet;
drawing the heated material sheet into a molded cavity to form a container; and
cooling the container.
25. The method of claim 24, wherein providing the material sheet comprises forming the material sheet.
26. The method of claim 24, further comprising:
separating and releasing the cooled container from the molded cavity.
27. The method of claim 26, further comprising:
filling the container with a product; and
sealing the container.
28. The method of claim 24, wherein said container comprises a container wall having a thickness from about 0.1 mm to about 3.0 mm.
29. The method of claim 24, wherein the one or more thermoplastic polyolefins are selected from the group consisting of polypropylenes, polyethylenes, and any combinations thereof.
30. The method of claim 24, wherein the one or more amorphous polymers are one or more cyclic olefin copolymers, polyamides, polyvinyl chlorides, polyetherimides, polyamideimides, polyarylates, or any combination thereof.
31. The method of claim 24, wherein the film is a mono-layer film.
32. The method of claim 24, wherein the film is a multi-layer film.
33. The method of claim 24, wherein the material sheet further comprises one or more barrier layers.
34. The method of claim 24, wherein the material sheet further comprises one or more adhesive layers.
35. The method of claim 24, wherein the material sheet further comprises one or more additives.
36. The method of claim 24, wherein the one or more thermoplastic polyolefins are present in the film in an amount from about 50 to about 95 percent by weight of the film.
37. The method of claim 24, wherein the one or more amorphous polymers are present in the film in an amount from about 5 to about 50 percent by weight of the film.
38. A roll of film for forming a thermoformed container, said roll of film comprising the material sheet of claim 1.
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Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2008136970A1 (en) * 2007-05-02 2008-11-13 Polyplastics Co., Ltd Thermoformed articles from sheet incorporating cycloolefin copolymer

Patent Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2008136970A1 (en) * 2007-05-02 2008-11-13 Polyplastics Co., Ltd Thermoformed articles from sheet incorporating cycloolefin copolymer

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
R. JESTER: "Cyclic Olefin Copolymer Enhances Polyolefin Blends for Film Packaging", 1 May 2011 (2011-05-01), XP002751240, Retrieved from the Internet <URL:http://www.ptonline.com/articles/cyclic-olefin-copolymer-enhanced-polyolefin-blends-for-film-packaging> [retrieved on 20151102] *

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