US20060255049A1

US20060255049A1 - Stretch blow-molded stackable tumbler

Info

Publication number: US20060255049A1
Application number: US11/481,888
Authority: US
Inventors: Donald McCarthy; Samuel Belcher
Original assignee: Fort James Corp
Current assignee: Dixie Consumer Products LLC
Priority date: 2002-08-09
Filing date: 2006-07-06
Publication date: 2006-11-16

Abstract

The inventive drinking vessels are prepared by stretch blow-molding a preform and exhibit increased Rigidity as well as elevated, preferably relatively uniform crystallinity. A preferred method of making blow-molded stackable drinking vessels includes expanding a preform both axially and radially to make an intermediate article with a neck, a transition portion and a tumbler portion. The transition portion and neck are severed from the tumbler which is then fortified around its upper aperture which is larger than its base.

Description

CLAIM FOR PRIORITY

This application claims the benefit of the filing date of U.S. Provisional Patent Application Ser. No. 60/402,314, filed Aug. 9, 2002. This application also claims priority to U.S. patent application Ser. No. 10/635,722, filed Aug. 6, 2003. The disclosures of each of these applications are incorporated herein in their entireties by this reference.

TECHNICAL FIELD

The present invention relates generally to drinking vessels and in preferred embodiments to a stretch blow-molded tumbler formed from an injection molded preform which is expanded radially and axially to form the tumbler. The tumblers exhibit high Rigidity, orientation and relatively high crystallinity.

BACKGROUND

In quick service restaurants, one of the highest margin items offered is the fountain beverage. In many cases, it is possible for the quick service restaurant owners to boost their sales of beverages by providing promotional cups either with printing tied to some media phenomenon, such as a popular children's movie or by offering cups in an unusual configuration. However, the ability to offer cups in unusual configurations or shapes is greatly limited by the technology currently used to produce such cups. In particular, injection-molding is relatively inefficient in use of materials when cups are formed from polymeric resins, while injection blow-molding is best applied to only a limited range of polymers and vacuum thermoforming produces a relatively weak cup. The cups produced by these methods are usually limited to traditional straight taper designs and are usually not transparent, particularly in large sizes as are typically employed in connection with promotional cups.
We have found that we can produce high strength cups with improved attributes from relatively small amounts of resin using a stretch blow-molding technique followed by a rim fortifying process. In particular, these cups have high Rigidity as the stretch blow-molding process orients the polymer axially as well as radially during the forming process and thereby increases the Rigidity of the cup considerably as compared to cups prepared by technologies that do not orient the polymers in both directions. A stretch blow-molding process makes it possible to use much higher molecular weight polymers and can induce increased crystallinity. Therefore the cups produced are stronger for this reason as well. Unique product benefits include: unmatched strength, clarity, printability, and the versatility to make reverse taper shapes or blow-molded embossed sidewall designs or logos. As will be appreciated from the comparisons described hereinafter, the cups or tumblers of the invention exhibit improved properties, especially Rigidity as compared with conventional cups. For example, there is reported in U.S. Pat. No. 6,554,154 to Chauhan et al. Rigidity data for thermoformed cups which are five times (5×) lower at 1 inch deflection than Relative Cup Rigidity values realized with the invention at 1 inch deflection.
The following patents are generally illustrative extrusion and injection blow-molding art, the disclosures of which are incorporated herein by reference.
Blow-molded containers are well known in the form of bottles, cans, jars and the like. There is disclosed in U.S. Pat. No. 6,237,791 to Beck et al. a method of making wide mouth containers by way of stretch blow-molding, which containers include threads or flanges so they may be used as jars or “hot-fill” food containers. The containers are prepared by stretch blow-molding a bottle, heat-setting the bottle and removing the upper neck portion. In some embodiments a curled rim is provided about the upper opening of the container by way of heating the upper sidewall of the bottle to or above its glass transition temperature, Tg, and curling the sidewall to form a curled rim. The containers may have a base with an annular peripheral chime surrounding an inward sloping base portion if so desired. See U.S. Pat. No. 4,889,752 to Beck.
U.S. Pat. No. 4,665,682 to Kerins et al. discloses a method of making polyester containers including blow-molding a bottle and severing the upper portion to make a jar or can.
U.S. Pat. No. 4,559,197 to Dick et al. discloses a method and apparatus for flanging a tubular polyester article in order to make a polyester can. The flange is used for sealing the can with a curled end unit as is well known in the art.
Stretch blow-molding is perhaps one of the most widely employed methods for making blow-molded bottles; however, the method is not believed to have been employed to make stackable drinking vessels. Rather, plastic blow-molded cups have been produced by the method of U.S. Pat. No. 4,540,543 to Canada Cup, Inc. where a stretch-rod is not used and the preform has a large opening. This process is more intricate to coordinate than stretch blow-molding processes and does not utilize generally available molding equipment since the injection-molding and blow-molding operations are practiced concurrently. Moreover, the process of the '543 patent does not extend the length of the injection molded parison and thus generally requires a relatively thin-walled parison which, in turn, restricts the selection of polymer material utilized in the process. So also, the process of the '543 patent does not include heating the parison sufficiently to relieve molded-in stress.

SUMMARY OF INVENTION

The tumblers of the invention are typically relatively rigid including a base, a sidewall and an upper aperture preferably prepared by stretch blow-molding an injection-molded preform at blow-up ratios of 3 or more. The tumblers exhibit a Rigidity Index of more than 1.25 lb_ffluid oz./gram at ⅔ cup height and ¼ inch sidewall deflection. Rigidity Indices of about 1.35, 1.4 and higher are still more preferred; Rigidity Indices from about 1.4 to about 2 are typical. The Relative Cup Rigidity is equal to the Rigidity Index for PET tumblers made of the reference resin; but may differ somewhat for resins of different composition. As used herein, PET per se refers to polymer resins consisting essentially of ethylene terephthalate repeat units, that is, over about 90 mole %; while other PET polymers may have more comonomer(s) as hereinafter discussed.
The tumblers typically exhibit a Rigidity of at least 4 or 5 lb_fat ⅔ cup height and 1 inch sidewall deflection as is seen in Table 6 hereinafter. A weight to volume ratio of less than about 1.2 gram/oz. is preferred; the volume being the contained volume of the tumbler. Weight to volume ratios of about 1 g/oz. or less are still more preferred. The inventive process provides relatively high crystallinity in the sidewall as will be seen from the calorimetry data which follows. Crystallinities of 20%, 25% and higher may readily be achieved with PET. The high Rigidity makes the process especially suitable for large tumblers of low weight. Tumblers of 20 fluid oz. volumes, 30 fluid oz. volumes and more are advantageously fabricated in accordance with the invention.
The Rigidity Index (hereinafter defined) of the cups of the invention tend to be significantly higher than those of other disposable cups. This is perhaps better appreciated by reference to FIG. 1, where it is seen the cups of the invention exhibit Rigidity Index Values of 1.4 and higher while values of 1.2 and lower were observed for other products.
One preferred method of making a blow-molded tumbler includes: (a) injection-molding a preform provided with a neck portion, a body portion and a bottom portion; (b) blow-molding the preform to form a first intermediate article therefrom wherein the preform is expanded radially as well as axially, the intermediate article being characterized by having a neck portion corresponding to the neck portion of the preform, a transition portion adjacent the neck portion of the first intermediate article and a tumbler portion adjacent the transition portion thereof, the tumbler portion of the first intermediate article being further characterized by having a base formed from the bottom portion of the preform and a sidewall formed from the body portion of the preform; (c) severing the tumbler portion of the first intermediate article from its transition portion to form a second intermediate article having a base corresponding to the base of the first intermediate article and a sidewall extending upwardly therefrom to define an upper aperture, the aperture being generally larger in area than the base of the second intermediate article such that the tumbler portions are stackable; and (d) fortifying the sidewall of the second intermediate article around the upper aperture to form the tumbler. Typically the step of blow-molding the preform includes, reheating the preform after it is injection molded, stretching the preform with a solid or hollow stretch rod prior to blow-molding, and then blow-molding the bottle, usually first with a low pressure and then with high pressure. Alternatively, uniform pressure may be used, but this is not preferred for the present invention. Generally, the first intermediate article has an axial stretch ratio of 1.5 to 7 and a hoop stretch ratio of 1.5 to 10. In some cases, the first intermediate article has an axial stretch ratio of 2.0 to 3.5 times and a hoop stretch ratio of 1.5 to 4. A blow-up ratio (hereinafter defined) of at least 3 is desirable, typically a blow-up ratio of at least 5 is used. Blow-up ratios of from about 7.5 to about 14 with respect to the preform are preferred in some cases; for instance, the first intermediate article may have a blow-up ratio of from about 9 to about 12. The tumblers or cups of the invention are stackable because their bases have a perimeter that is smaller than the inner perimeter of their upper apertures and of suitable shape, such that one tumbler may be stacked with a like tumbler. Preferably, the tumbler's perimeter from its base up to about 60% of its height is likewise smaller than the interior of its upper aperture so that the lower 60% at least fits within a lower adjacent tumbler in a stack. In many cases, it is desirable that the tumbler's perimeter at its base and its perimeter up to at least 90 or 95% of its height is smaller than the interior of its upper aperture such that the tumblers are compactly stackable.
While any suitable resin composition may be used, resins without mineral filler are preferred in many embodiments.
Typically, the tumbler has a generally circular cross-section and comprises in some embodiments a polyethylene terephthalate (“PET”) polymer. The tumbler may consist essentially of polyethylene terephthalate having an intrinsic viscosity of from about 0.55 to about 1.05. An intrinsic viscosity of about 0.72 or greater is sometimes desirable. Typically, the preform has a weight of from about 10 grams to about 200 grams, whereas the tumbler has a contained volume of at least about 7 fluid oz. Sometimes the preforms weigh between about 25 grams and 100 grams. A tumbler volume of from about 12 oz. to 64 oz. is typical as is an outward taper from its base to its upper aperture of from about 2° to about 12°. A tumbler volume of from about 20 to about 35 fluid oz. is typical in many embodiments, especially for promotional cups. In some cases a taper from the tumbler base to its upper aperture of from about 3° to about 8° is preferred and the tumbler has a reverse (or inward) taper over a portion of its sidewall. Preferably, the tumbler has a generally smooth sidewall adjacent its fortified rim, free from thread features. Generally, the tumbler rim has a lateral thickness of from about 1.5 to about 10 times the thickness of the sidewall adjacent its fortified rim. The tumbler sidewall usually has a wall caliper of generally from about 0.005 inches to about 0.100 inches, covering the range of lightweight, disposable tumblers to heavy weight, reusable products. Reusable products may have a wall caliper of from about 0.025 inches to about 0.09 inches; typically in the range of from about 0.040 to about 0.080 inches; significantly thicker than blow-molded bottles, for example.
The tumblers may be made in a variety of shapes including oval cross-sections, rounded square cross-sections, rounded triangular cross-sections and so forth. A tumbler may have a cross-sectional shape selected from the group consisting of non-circular ovals, rounded polygons and combinations of curved and linear segments forming a closed perimeter. Likewise, there may be included features such as grips, handle portions or other surface features. For example, one could include tooling with insertable logos in the blow-molds for producing products for different promotional campaigns.
In a particularly preferred embodiment, the first intermediate article is provided with a circumferential cutting notch or knife guide joining the transition portion with the tumbler portion, as well as provided with a circumferential groove in the transition portion of the first intermediate article adapted to receive a drive member for rotating the article during the step of severing the tumbler portion therefrom.
The step of fortifying the sidewall of the second intermediate article around the upper aperture may involve shaping the dome portion of the bottle such that the angle of the severed end remaining on the intermediate article will facilitate the formation of a fortified rim. The action required to form the fortified rim may range from pinching two sidewalls together to reshaping the severed end such that the end of the fortifying portion follows a curvilinear path, which may be varied up to 360° or more. In a typical case, the tumbler is made from a polyethylene terephthalate polymer and the fortified lip is provided with a die or other curling tool, such as a curling screw, maintained at a temperature of from about 275° F. to about 350° F. A die maintained at a temperature of from about 285° F. to about 330° F. is suitable for PET, which may also be cold curled. The curling tool may be a worm gear-type screw, a paper cup brim forming die, a can double seamer, or a curling die which may be operated from about typical room ambient temperatures to about 325° F. for PET. In typical cases, the curling tool is operated from ambient temperatures up to the glass transition temperature of the polymer.
The step of fortifying the sidewall of the second intermediate article around the upper aperture may alternatively include applying a rim-forming member to the sidewall around the upper aperture, preferably wherein the rim-forming member is the same material as the tumbler. The rim-forming member may be an end unit including a lid portion, wherein at least a part of the lid portion is removable and includes a removable pull-tab. The rim-forming member may have a U-shaped profile. Likewise, the sidewall of the tumbler around the upper aperture may be configured to have a downwardly projecting U-shaped terminal portion interlocked with an upwardly projecting U-shaped terminal portion of the rim-forming member.
The tumbler portion of the first intermediate article may be provided with a flange projecting inwardly or outwardly from its sidewall joining the tumbler portion of the first intermediate article to the transition portion thereof. The flange may project downwardly as well and is generally configured to be incorporated into the fortified rim of the tumbler and facilitate formation of the tumbler rim.
The preform from which the tumbler is made need not be threaded. Inasmuch as the neck portion of the first intermediate article is severed in any event, it is only necessary to have some means for securing the preform during blow-molding; in this respect, either a flange projecting outwardly from the preform at its upper portion or a recess formed therein is sufficient.
In another aspect of the invention, there is provided a stackable tumbler produced by blow-molding a preform wherein the preform is expanded radially and axially to form the tumbler which is characterized by a sidewall, an upper aperture and a base wherein the upper aperture is of generally larger area than the base and the sidewall is provided with a fortified rim around the upper aperture. Here again, the tumbler generally has an axial stretch ratio of 1.5 to 7 times and a hoop stretch ratio of 1.5 to 10 times. Usually the tumbler has an axial stretch ratio of 2.0 to 3.5 times and a hoop stretch ratio of 1.5 to 4 times with respect to the preform. The tumbler may have a weight of from about 10 to about 200 grams and typically has a contained volume of at least 7 fluid oz. as noted above; sometimes a contained volume of at least about 12 oz. up to typically 64 oz., but sometimes as high as 96 oz., which is beyond the normal consumption needs of an individual but which may be fitted with a handle or carrying device and a lid with a pour spout.
Optionally, the method of the invention includes a heat-setting step in connection with the blow-molding of the first intermediate article. The first intermediate article is heat-set in the blow-mold by controlling the temperature of the blow-mold and the “residence time” of the first intermediate article in the mold. This procedure is particularly advantageous for reusable cups which are relatively thick-walled. The residence time is (for practical purposes) the time in seconds from commencing either stretching or blowing of the preform to the mold being opened for removal of the blow-molded container. The residence time and mold temperature may be controlled to achieve the desired crystallinity, which may be from about 25 to about 45% (on a weight basis) and in some embodiments from about 35% to about 42%. A preferred method of determining crystallinity is to use differential scanning calorimetry. Alternatively, ASTM Method 1505 provides a density gradient method. The temperature of the blow-mold on its portion corresponding to the sidewall of the tumbler is generally maintained at a temperature of from about 200° F. to about to about 350° with from about 250° F. to about 280° F. being typical for heat setting. The temperature of the blow-mold at its portion corresponding to the base of the tumbler is generally maintained at a temperature of at least about 150° F. during heat-setting and typically at a temperature of at least about 165° F., which is less than the temperature of the mold at its portion corresponding to the sidewall of the tumbler. Residence times for heat-setting cycles may be from 0.5 to 5 seconds with from about 1 to about 3 seconds being typical.
The tumblers may be made from a multilayer or laminated preform which contains, for example, a barrier layer of ethylene vinylalcohol, polyamide such as nylon or vinylidene chloride polymer. Other functional layers might include a thermally conductive layer, for example, a layer containing heat conducting materials such as carbon black, carbon nanotubes (buckytubes), metallic fibers or particles, or inherently conductive polymers. In some cases, if delamination is sought, adjacent layers may be formed from polymers which form a low adhesion interface such as PET and polypropylene or reactive agents may be used to generate a gas to foam the layers and/or separate them. Suitable reactive agents may be foaming agents such as sodium bicarbonate on one layer and citric acid on an adjacent layer. Heat-setting the article in the mold can be especially advantageous in connection with multilayer preforms wherein one layer has not been heated above its orientation temperature during the blow-molding process. For example, at PET/PP multilayer preform could be blow-molded at 200° F. or so which may be sufficient to orient the PET which typically has an orientation temperature of from about 190° F. to 240° F., but not sufficient to orient the polypropylene, which has an orientation temperature of from about 250° F. to about 280° F. If the article is heat set at 275° F. or so, the orientation temperature of the polypropylene may be exceeded and the polymer will orient in the desired configuration.
The multilayer preform may contain two contiguous layers of polymer with different compositions, but including a common monomeric repeat unit to improve compatibility and adhesion of the various layers while providing for a spectrum of properties. For example, there could be provided an interior layer of polypropylene copolymer which is relatively stiff and an outer layer of polypropylene copolymer which is relatively soft to improve “hand feel” of the tumblers.
The tumblers of the invention may be made of any suitable material in addition to PET. Suitable materials may include: polystyrene; polycarbonate; styrene; acrylonitrile; polyvinyl chloride; polyolefin polymers including polypropylene, cyclic polyolefin copolymers, polyethylene, polybutylene polymers and the like; polyamide polymers; polysulfones; polyacetals; polyarylates; polyacrylonitrile -stryrene copolymers; polyolefin ionomers; styrene-acrylonitrile copolymers; environmentally degradable polymers and mixtures thereof, as is described hereinafter. The inventive method provides remarkable improvements in many cases. For example, a styrene tumbler made by the inventive method resists splitting upon flexing to a remarkable degree as compared with polystyrene cups made by other methods.
In some embodiments, the tumblers of the invention can be made relatively thick-walled, e.g., a wall thickness of greater than 25 thousandths of an inch such that it is not necessary to fortify the rim; rather the tumbler portion may simply be severed from the upper portion of the intermediate article and the rim optionally smoothed with a flame treatment, abrasive, or other honing technique. Of course, curling the rim or flanging it with a hot tool will likewise provide the needed smoothness after cutting the tumbler from the transition section.
Still yet another technique for making the inventive cups is by molding them directly in a stretch blow-molding process of the type described in U.S. Pat. No. 4,731,011 to Nakamura et al., the disclosure of which is incorporated herein by reference. In this process the rim of the preform is not expanded and corresponds to the rim of the tumbler so that severing a portion of an intermediate article is not required. Generally, the rim of the tumbler is from about 1.2 to 5 times the thickness of the adjacent sidewall of the tumbler when employing this process as noted hereinafter.
These and other features and advantages of the present invention will be better understood by considering the following description and appended drawings.

BRIEF DESCRIPTION OF DRAWINGS

The invention is described in detail below with reference to the drawings wherein like numerals designate similar parts and wherein:
FIG. 1 is a comparison of observed Rigidity Index values, comprising disposable cups of the invention with various other cups.
FIG. 2A is a schematic view in elevation of a preform used for making a tumbler of the invention;
FIG. 2B is a schematic view in elevation of an alternate design of a preform used for making a tumbler of the invention;
FIG. 3 is a schematic view in elevation of a blow-mold with a stretch rod and an intermediate article of the invention;
FIG. 4A is a schematic view in elevation of a first intermediate article of the invention;
FIG. 4B is a partial schematic view in elevation of another configuration of a first intermediate article of the invention;
FIG. 4C is yet another partial schematic view in elevation of still another configuration of a first intermediate article of the invention;
FIG. 5 is a schematic view in elevation of a second intermediate article of the invention wherein the transition portion has been severed;
FIGS. 6-10 are schematic diagrams illustrating providing a lip curl to the second intermediate article of FIG. 4;
FIG. 11 is a perspective view of a tumbler of the invention;
FIGS. 12 and 13 are schematic diagrams illustrating a fortified rim of a tumbler of the present invention provided by way of using a U-shaped rim forming member;
FIGS. 14-17 are schematic diagrams illustrating a lidded tumbler of the invention wherein the lid is formed with a double sealing end unit; and
FIG. 18 is a schematic view in elevation of another blow-mold for fabricating biaxially-oriented tumblers of the invention.

DETAILED DESCRIPTION

The invention is described in detail below with reference to numerous embodiments, which description is provided for purposes of illustration only. Modifications to those embodiments, within the spirit and scope of the present invention, set forth in the appended claims, will be readily apparent.
Unless otherwise defined or the context clearly indicates a more specific meaning, terminology as used herein is given its ordinary meaning. “Tumbler”, for example, refers to a stemless drinking vessel. “Taper” refers to the angle with a vertical defined by a line from the base of a tumbler to its rim. A “polyethylene terephthalate” or “PET” polymer is a polymer having more than 50 mole % polyethylene terephthalate repeat units, whereas a polymer or material “consisting essentially of” polyethylene terephthalate has at least about 90% on a molar basis polyethylene terephthalate repeat units. Such materials are sometimes referred to in the art as “bottle resin” and may include, for example, isophthalic residues if so desired. “Caliper” refers to the thickness of an article or the thickness at a particular point in the article as the context indicates.
“Axial” and “hoop stretch” ratios as used herein are characteristics of a blow-molded article with respect to its preform and express the amount of expansion a preform undergoes to make the blow-molded article. “The Blow-Up Ratio” (BUR) is a combined ratio in which the axial stretch ratio is multiplied by the hoop stretch ratio to give an overall or blow-up ratio. The equations for calculating the axial, hoop, and blow-up ratios are as follows: $\begin{matrix} Axial Stretch Ratio = \frac{La}{Lp} \\ Hoop Stretch Ratio = \frac{Da}{Dp} \\ Blow - Up Ratio (BUR) = (Axial Stretch Ratio) \times (Hoop Stretch Ratio) \end{matrix}$
wherein:

Da=the maximum inside diameter of the article at the midpoint height
Dp=the minimum inside diameter of the preform at the midpoint height
La=the length of the article below the neck (typically measured from the capping ring minus 0.100 inch to the top of the push-up on the inside of the article)
Lp=the length of the preform below the neck (typically measured from the capping ring minus 0.100 inch to the bottom of the inside surface of the preform)
For articles or preforms with a non-circular cross-section, the diameters employed for purposes of calculating the draw ratio may be based on the corresponding cross-sectional area, for instance, the diameter may be taken as the square root of 4/π times the corresponding area.

When a polymeric material has a higher molecular weight or the polymer is oriented, many of the attributes desired in the products are enhanced; because increased molecular weight, increased orientation, and increased crystallinity work predominantly toward enhancing the desirable physical properties of the products, it is desirable to devise fabrication procedures which allow for realizing the potential of the material. Table 1 below lists the physical properties and other attributes of polymeric articles and whether that property increases or decreases with increasing molecular weight, increased orientation, or increasing crystallization.

TABLE 1


Property Relationships With Molecular Weight,
Orientation and Crystallization

	Increasing
	Molecular	Increased	Increasing
Property	Weight	Orientation	Crystallization

Tensile Strength	+	+	+
Modulus	+	+	+
Yield Strength	+	+	+
Elongation	+	−	−
Impact (Toughness)	+	+	+/−
Hardness	+	+	+
Abrasion Resistance	+	+	+
Chemical Resistance	+	+	+
Environmental Stress	+	+	+/−
Cracking Resistance
Barrier Properties	+	+	+
Adhesion	−	−	−
Solubility	−	−	−

+ Property increases
− Property decreases

Another benefit of the stretch blow-molding process is the annealing that takes place to relieve the stress in the injection-molded preform. The result is primarily a stress-free product that is highly biaxially orientated. This property is of particular interest in heavier weight tumblers that will be washed and reused in a casual dining setting where environmental stress cracking results from dishwasher detergents. Plastic cups that have problems with detergent stress cracking have limited life cycles and, thus, provide a lower value to the purchaser. The two most critical parameters that will reduce or eliminate environmental stress cracking (ESCR) are increased molecular weight (decrease in melt flow) and stress free products. Polycarbonate (PC), for example, has an ESCR problem with strongly alkaline detergents. Heavy weight polycarbonate tumblers (used in casual dining restaurants) made by the injection blow-molding process using 22 melt flow PC begin to stress crack (¼ inch cracks) after 6 dish washer cycles. When the molecular weight is increased to 10 melt flow PC, the equivalent level of stress cracking does not appear until after the 34^thwash cycle. However, the limit on the ability to increase molecular weight is defined by the wall thickness of the product and the height of the tumbler. The flow properties of the polymer need to allow timely filling of a multi-cavity injection mold. As the size of the cup increases in volume or height, increasing the molecular weight is difficult with prior art processes such as that of the '543 patent noted above (“IBM” process) because the preform is the length of the cup and when it is blown it is only stretched in the hoop direction. The preform stresses are not annealed out in the IBM process and can only be controlled by rigorous temperature control in the mold. Once made, the solidified, but still hot, preform is shuttled to a blow cavity and blow-molded. ESCR related problems in polycarbonate made by the IBM process are as follows: blow-up ratios for the IBM process are low and uniaxial; stress-free parts are not produced; and the polycarbonate is not “blown” in the ideal temperature range for orientation.
Heavy weight polycarbonate cups made by the two-step stretch blow-molding process eliminate these disadvantages. The stretch blow-molding process uses a higher molecular weight polycarbonate resin; the reheating process anneals the stress out of the preform; and the preform temperature can be precisely controlled so that blow-molding takes place in the ideal temperature range for orientation. When these conditions are met the tumbler or cup will have greatly reduced molded-in stress and greatly improved ESCR performance.
The various features of the invention will be better understood by reference to the drawings.
There is shown in FIGS. 2A and 2B alternative designs of an injection molded preform 10 having generally a preform length 12 below its neck 14. Neck 14 is provided with a flange 16 as well as optional threads indicated at 18 in FIG. 2A. The threads and/or flange 16 may be used to hold the preform in place during processing. A preform designed specifically for blow-molding a tumbler as shown in FIG. 2B has a cost advantage in that no threads are needed in the neck area and only a small flange is needed to hold the preform in the mold. Cost savings would result from (1) reducing the weight of the preform and (2) lowering the mold costs by eliminating thread splits. Typically, soda bottle preforms weigh about 26 grams for a 20-oz. bottle and 48.5 grams for a 2-liter bottle. Tumblers of this invention may vary considerably in weight depending on the intended final use. If the intended use were to provide a foodservice customer with a take-out tumbler for soda, then a lightweight tumbler would be appropriate. If the customer is a dine-in customer who uses a tumbler that the casual dining restaurant washes and reuses multiple times, then the tumbler needs to be made using a heavy weight construction for durability. Therefore, the weight range from lightweight use to a heavy weight use can be considerable. For example, a 22-oz. tumbler for take-out could weigh as little as 16-18 grams and a reusable tumbler of the same size could weigh 50 to 95 grams. Preform 10 may be relatively thick, having a wall thickness 20 of generally from 0.060 inches to 0.180 inches, which need not be a constant thickness over its body portion 22 and bottom portion 24; the thickness can be optimized to provide enhanced Rigidity about ⅔ of the way up from the base by thickening at this level.
FIG. 2B depicts a multilayer preform 10 provided with an outer layer 17, an inner layer 19 and an intermediate layer 21 which may be a barrier layer if so desired. So also, contiguous layers may be provided with reactive chemicals and so forth as noted above, or may be materials such as polypropylene and PET which do not readily adhere to one another. If so desired, one or more of the layers may be further provided with functional attributes such as high or low thermal conductivity if so desired. So also, adhesives may be employed when delamination is to be avoided.
Preferably, the preform comprises a PET polymer and in preferred embodiments is made of bottle resin having an intrinsic viscosity or IV (a measure of molecular weight) of from about 0.55 to about 1.05 as measured according to ASTM D4603, Standardized Test Method for Determining Inherent Viscosity of PET. This test standard also establishes a method for calculating Intrinsic Viscosity. The primary equipment used is a capillary viscometer, such as the Cannon Ubbelohde Type 1 B Viscometer referred to in ASTM D4603.
The IV or intrinsic viscosity of a PET sample is a relative number and represents a measure of its average molecular weight. An IV is determined by dissolving between ¼% and ½% PET in a solvent and measuring the time required for 100 ml of the solution to flow through a capillary. Concentration and time are then used to mathematically compute the IV. The term “inherent viscosity” refers to any IV determined at a specific concentration of the PET solution. A series of IV's are determined at varying concentrations and the data plotted on a curve of IV vs. concentration. The curve is extrapolated back to zero concentration, and this point is defined as the “intrinsic viscosity.”
Preform 10 is typically preheated to a temperature of from about 1 90° F. to 240° F. or so when made from PET so that it may be blow-molded as shown schematically in FIG. 3.
The blow-up ratio (BUR) for PET tumblers of this invention generally range from about 3 to about 14.
FIG. 3 illustrates schematically a blow-mold 30 having mold halves 32 and 34 as well as a stretch rod 36 used to stretch preform 10 in a stretch blow-molding step. Preform 10 is positioned in mold 30 and stretched with rod 36 and a blow-head provides pressurized air into the interior of the preform. The preform is thus expanded axially as well as radially in mold 30 to form a first intermediate article 40 (FIGS. 3, 4A, 4B, 4C) having a length 42 and a maximum outside diameter 44.
When using a preform having a length 12 of four inches or so, intermediate article 40 may have a length 42 of 8 inches or so. Diameter 44 may be about 3.5 inches when using a preform having an inside diameter 46 of an inch or so. The axial and hoop stretch ratios with respect to preform 10 are thus: $Axial Stretch Ratio = \frac{8}{4} = 2$ $Hoop Stretch Ratio = \frac{3.5}{1} = 3.5$ $Thus, the Blow - Up Ratio (BUR) is (Axial Stretch Ratio) \times (Hoop Stretch Ratio) or (2 \times 3.5) = 7$
Stackable tumblers of the invention may be blow-molded from clear materials such as: PS (polystyrene), PC (polycarbonate), SAN (styrene acrylonitrile), PVC (polyvinyl chloride), PP (polypropylene), nylon, COC (cyclic polyolefin copolymers), and other polyolefins, and may be combined in multi-layer constructions with barrier materials such as ethylene vinyl alcohol (EVOH), Nylon MXD6 from Mitsubishi Gas Chemical Company, Inc., or with oxygen scavenging materials and with adhesive layers as appropriate. Other suitable polymers may include polysulfones, polyacetals, polarylates (wholly aromatic polyesters), ionomeric polyolefins sold under the tradename Surlyn® and environmentally degradable polymers. Environmentally degradable plastics generally include those which undergo significant changes in their chemical structure under specific environmental conditions, such polymers include oxidatively degradable polymers, photodegradable polymers, and biodegradable polymers. A biodegradable plastic polymer is a material in which the degradation results from the action of naturally occurring microorganisms such as bacteria, fungi and algae. Suitable polymers are described in Volume 19 of the Kirk-Othmer Encyclopedia of Chemical Technology, 4^thEd., pp. 983-996 (Wiley) the disclosure of which is incorporated herein by reference. Carboxylated polymers are generally a preferred class, including poly(lactic acid), polyanhydrides, functionalized natural polymers and so forth. Insofar as the tumblers of the invention are concerned, the polymer selected must have sufficient moisture resistance for the products' intended end uses. Preferred biodegradable polymers including polylactic acid, polyhydroxybutyrate and polycaprolactones which may optionally be melt-blended with PET.
Suitable polymer compositions include melt blends of cycloolefin copolymers of norbomene and ethylene with various polyethylene polymers. Cycloolefin copolymers are described in U.S. Pat. No. 5,698,645 to Weller et al., the disclosure of which is incorporated herein by reference. The various polyethylene polymers referred to herein are described at length in the Encyclopedia of Polymer Science & Engineering (2 Ed), Vol. 6, pp. 383-522, Wiley 1986, the disclosure of which is also incorporated herein by reference. HDPE refers to high density polyethylene which is generally linear and has a density of generally greater than 0.94 up to about 0.97 g/cc. LDPE refers to low density polyethylene which is characterized by relatively long chain branching and a density of about 0.912 to about 0.925 g/cc. LLDPE or linear low density polyethylene is characterized by short chain branching and a density of from about 0.92 to about 0.94 g/cc. Finally, intermediate density polyethylene (MDPE) is characterized by relatively low branching and a density of from about 0.925 to about 0.94 g/cc. Unless otherwise indicated, these terms have the above meaning throughout the description and claims.
The materials may be tinted; colored with opaque organic or inorganic pigments; contain fillers such as calcium carbonate, talc, mica, nano-size particulates, flame retardants, nucleating agents, clarifiers, antistats, foaming agents; and/or combined with blends of any of the listed polymers with or without compatibilizing agents or in combination with biodegradable polymers.
Monolayer performs may contain multiple colors of dispersed regions of colorants so that the stretch blow-molded article has the visual effect of swirl or marbleized patterns of distinguishable colors. Multilayer performs may contain different colors in layers of different thickness so that, when blow-molded, the colors of the thicker layers predominate as the background color and the thinner layer produces color differentiated patterns. Dispersed flakes or particles that add a sparkle effect to the blow-molded article may be added in combination with colorants in monolayer or multilayer constructions.
Nano-size particulates may be clays, conductive carbons, silicas, titanium dioxide, aluminum trihydrate, or similar sized materials chosen to enhance a specific property such as modulus, tensile strength, fire retardancy, insulation, conductivity, visual appearance, or tactile feel. The process of the present invention is particularly useful in connection with transparent drinking containers from filled resins which have been characterized as “nano-composites”. Nano-composites are reinforced resins which comprise the resins enumerated above and nanometer-sized filler particles. It has been found that resins containing small amounts of approximately 2-6% of the nanometer-sized particles can provide improvements in mechanical and thermal properties, improvements in gas barrier and flame resistance and do not reduce the light transmission of the resins inasmuch as the nanometer-sized particles are in the same size range as visible light wave lengths. A discussion of nano-composites is provided in Plastics Technology, June, 1999. Accordingly, nano-composites can advantageously be used to injection blow-mold drinking containers such as tumblers and the like. Thus, not only would the transparent nature of the resins be maintained, but the strength of the resin could be improved. For polystyrene, the use of a nanometer-sized filler could improve the strength of the resin and provide more uses of this resin than for just disposable tumblers. Nylon composites are likewise of interest. At present, nanometer-sized clay has been used to form nano-composites. For example, montmorillonite, which is a layered alumino-silicate having individual platelets that measure on the order of 1 micron diameter and have an aspect ratio of 1,000:1 have been added to nylon. Suppliers of the nanometer montmorillonite are Nanocor, Inc. and Southern Clay Products. For some of the above listed resins, it may be useful to chemically modify the surface of the montmorillonite inasmuch as this hydrophilic clay may not be compatible with the more hydrophobic resins. Surface treatments can include exchanging the inorganic cations on the surface of the clay with materials which can induce hydrogen bonding with the resin including hydrogen cations, ammonium cations, silane cations and the like. Other fillers can be formed chemically or ground to the appropriate size and used as fillers for the injection blow-moldable resins of this invention. For example, inorganic or organic pigments such as zinc oxide, or titanium oxide can be used. Even plastic fillers can be provided in nanometer sizes and added to the blow-moldable resins. The nanocomposites can be formed by forming the resin itself in the presence of the nano-filler particles or by simply melt-compounding the formed resin with the nano-filler particles. During the melt-compounding method of forming nano-clay composites, it has been found necessary to delaminate the clay particles sufficiently so that the ultimate level of reinforcement and transparency can be achieved.
Preforms may be made of a single component such as PET, may be monolayer blends of different materials, or may consist of multi-layers designed to enhance specific properties or to provide a unique feature(s) in the final product. Examples of such unique features are as follows: the addition of a barrier layer for reducing oxygen, carbon dioxide, or water vapor transmission; the addition of a layer with increased thermal conductivity to speed the heating or cooling of the contents of the tumbler.
The addition of adjacent layers each containing a component of a reactive mixture that may be used to promote a property change at the interface of the two layers. An example of such a reactive mixture would be to have incompatible polymers such as PET and polypropylene injection molded into a two-layer preform with one layer containing sodium bicarbonate and the other layer containing citric acid. The desired effect at the interface would be to facilitate the separation of the two distinct layers that are formed in the tumbler made by the blow-molding process. The purpose of the layer separation is to allow the formation of an air gap between the layers. Such an air gap would provide insulation for the tumbler for keeping hot beverages hotter longer and would also increase the hold time for the customer. Similarly, cold beverages would stay cold longer and the outside of the tumbler would not sweat from moisture condensation. The rim fortification process would fix the two layers at the top of the tumbler and there may be an optional point of attachment at the original gate of the preform at the bottom of the tumbler.
In FIG. 4A, article 40 is formed from preform 10 and thus has at its upper portion neck 14 of preform 10, a transition portion 48 as well as a tumbler portion 50. Portions 48 and 50 correspond to the body portion 22 of preform 10 (radially and axially expanded) whereas a base portion 52 corresponds to bottom portion 22 of preform 10.
Base portion 52 is generally circular in most embodiments and has a diameter, D_b, that is smaller than the diameter, D_r, of the intermediate article at the portion of the intermediate article where the rim of the tumbler is formed.
An angle 54 is defined between a line 53 joining the outer edge of base 52 and the circumference of the upper portion of the tumbler with a vertical line 55 and is generally referred to as the taper or taper angle of the tumbler. The articles of the invention generally have an outward taper with increasing height as shown, since their upper apertures are larger than their bases. For purposes of brevity, this geometry is simply referred to as an “outward” taper, or simply taper.
Note that the tapered portion of the tumbler also has reverse (or inward) taper regions 58, 60, which would not be practical with forming techniques such as thermoforming or injection-molding.
Intermediate article 40 of FIG. 4A has formed in transition portion 48 a circumferential drive groove 62 suitable for receiving a drive belt 64 which may be used for rotating the article during severing of portion 48 from portion 50. To facilitate separation there is provided a circumferential notch 66 which is operable as a knife guide for guiding a knife 68 used for severing portion 50 from portion 48.
That is to say, article 40 shown schematically in FIGS. 3 and 4A is rotated by way of belt 64 while knife 68 is inserted in notch 66 in order to sever the tumbler portion 50 from transition portion 48 to produce a second intermediate article 70 as shown in FIG. 5.
Article 70 has a base portion 52 corresponding to base portion 52 of article 40 as well as the other features of tumbler portion 50 noted in connection with FIGS. 3 and 4A. There are optionally provided a plurality of flutes 72, 74, 76 in a sidewall 78 of article 70. Sidewall 78 extends upwardly from base 52 to define an upper aperture 80 which is generally circular and has diameter D_r. D_ris larger than D_bsuch that article 70 is stackable with like articles. To finish the tumbler, sidewall 78 is fortified around aperture 80 by one of a variety of techniques, including curling a lip portion 82 of article 70 to form a fortified rim as described in connection with FIGS. 6 and following. Note that articles 40 and 70 are optionally provided with an interior raised portion 84 which defines a chime 86 if so desired.
There is shown in FIGS. 4B and 4C alternate configurations of the first intermediate article provided with flanges as part of the tumbler portion to aid in the formation of a fortified rim. In these embodiments, article 40 has a neck portion 14, a transition portion 48, a tumbler portion 50 and optionally a knife guide notch 68. Sidewall 78 of tumbler portion 50 has at its upper portion a flange configured to be incorporated into the fortified rim of the tumbler. In FIG. 4B flange 79 projects outwardly and downwardly from the sidewall; downwardly that is, with respect to a horizontal line 81 from the sidewall. After transition portion 48 is severed, the flange may be utilized to form a rim either by curling it to the sidewall or by cooperation with a rim forming member.
In FIG. 4C a flange 83 projects inwardly and optionally downwardly with respect to sidewall 78; that is, downwardly with respect to a horizontal line 81 from the sidewall. Here again, after severing portion 48 the flange may be further curled and incorporated into the rim. It is not necessary to utilize a flange in order to provide a fortified rim as will be appreciated from FIGS. 6, 7, 8, 9, 10 and 11. Indeed, while horizontal flanges may be readily prepared, flanges with inclination with respect to the sidewall will require more complex mold design and operation, perhaps including severing the transition portion from the tumbler portion while the first intermediate article is still in the mold.
Referring to FIG. 6, lip portion 82 of article 70 is curled by upper and lower tools, 90, 99. The curling portion of upper tool 90 is indicated at 92. Die 92 and lower tool 99 may be heated to or maintained at a temperature of between 275° F. to about 350° F. during a curling operation as the tools are axially advanced towards each other as shown schematically in FIGS. 7, 8 and 9. It is desirable to rotate die 92 with respect to article 70 during the curling operation. If so desired, one may pre-heat the sidewall prior to curling as noted in U.S. Pat. No. 6,237,791 to Beck et al. or provide auxiliary radiant heating as indicated in FIG. 10 at 94 or insulate die portion 92 from the rest of tool 90 as indicated at 96 in FIG. 10; depending upon the temperatures and materials employed.
Lip 82 may be curled at 360° or more as seen at 98 in FIG. 9.
Another preferred tooling for providing a rim curl is to use a curling screw apparatus as disclosed in U.S. Pat. No. 6,164,949 to Lamson. This apparatus includes an oven and four co-rotating helical curling screws; alternatively, a like apparatus with a single curling screw is seen in U.S. Pat. No. 3,337,919 to Brown. The disclosures of the above patents are incorporated herein by reference.
A finished stackable tumbler 100 is shown in perspective in FIG. 11. Tumbler 100 has a curled fortified rim 102, sidewall 78 and base 52 corresponding to like parts of articles 40 and 70 described above. Upper aperture 80 is circular in shape and larger in diameter than base 52 so that tumbler 100 is stackable with like articles. The tumbler retains the molded-in features such as flutes 72, 74 and 76 as well as raised portion 84 and chime 86. Likewise, reverse taper regions are provided in sidewall 78; that regions where the diameter of the tumbler decreases with increasing height such as at 58 and 60.
Tumbler 100 is readily differentiated from jars or other containers in that it has a positive taper angle 54 as noted above and is free from threads adjacent its upper aperture 80. The fortified rim is distinguished from closure flanges and the like since it projects laterally a distance 104 which is relatively small with respect to the aperture diameter, typically from 1½ to 10 times the adjacent wall caliper.
Other modes of fortifying the tumbler rim may be employed. For example, there is shown schematically in FIGS. 12 and 13 a rim-forming member 110 with a U-shaped profile 112 folded over sidewall 78 of the tumbler. Member 110 is preferably of the same material as the tumbler and may be heat-bonded therewith to form a fortified rim structure 114 shown in FIG. 13.
There are numerous other options for fortifying the rim of a second intermediate article of the invention. Another method, for example, is to design the blow-molded first intermediate article so that its transition portion can be further severed so that a portion or band fashioned therefrom can be utilized as a rim-forming member such as member 110. Alternatively, the transition portion is designed so that it can function as a lid which also provides rigidity to a combined structure after removal from the first intermediate structure and recombination with the second intermediate structure. That is to say, the process of fortifying second intermediate article 70 may include providing a band or lid made from transition portion 48 of first intermediate article 40. This process may be more expedient than forming a lid or reinforcing member separately and more efficient in terms of material usage. Thus, the process of fortifying the second intermediate article of the invention around its upper aperture comprises fashioning a reinforcing member from the transition portion of the first intermediate article preferably selected from the group consisting of a band or lid and applying the reinforcing member so-produced to the second intermediate article around its upper aperture.
As a still further alternative, there may be provided an end unit such as end unit 116 shown in FIGS. 14, 15, 16 and 17 of the double seal type used on polyethylene terephthalate cans as are known in the art. To this end, there is provided a flanged container 118 having a flange 120 about its upper aperture 122, a sidewall 124 and a bottom 126. End unit 116 has a curled periphery 128 which is crimped about flange 120 to make a double seal as shown sequentially in FIGS. 14, 15. FIG. 16 is an enlarged schematic view showing the double seal joint wherein the tumbler is lidded with end unit 116. A preferred technique for applying the lid is to use a curling tool as disclosed in U.S. Pat. No. 4,559,197 to Dick et al., the disclosure of which is incorporated herein by reference. This results in a double seal with an upwardly U-shaped portion 130 defined by the lid and a downwardly U-shaped portion 132 defined by flange 120 after it is crimped.
The end unit may include a pull-tab 134 coupled to a localized removable portion indicated at 136, or, the lid may be weakened around its entire periphery as indicated at 138 in FIG. 17 which is a schematic top view of a lidded tumbler produced in accordance with the present invention. End unit 116 may be metal or plastic, but most preferably is thermoformed from the same material as the rest of the tumbler.
Still yet another method of making the tumblers of the present invention is a coordinated injection-molding, stretch blow-molding process as disclosed in U.S. Pat. Nos. 4,731,011 and 5,753,279 (Nissei). The process involves injection-molding preforms on a core and transferring the preforms to a blow-mold in some respects like the process of the '543 patent noted above; however, the preform is expanded both axially and radially to provide for greater orientation. The rim of the preform corresponds to the rim of the tumbler as is shown schematically in FIG. 18.
In FIG. 18 there is shown a mold 30 having mold halves 32, 34 as well as a stretch rod 36 used to stretch the preform. The preform is expanded to a height 42; however, the diameter 44 of the tumbler rim corresponds to the diameter of the upper portion of the preform from which it was made. Tumbler 40 is thus formed without the need for severing a portion of an intermediate article. Tumbler 40 is preferably provided with an injection-molded rim 41 which has a thickness greater than the thickness of the adjacent sidewall. The thickness of the rim is indicated schematically at 43, while the thickness of the sidewall is indicated schematically at 45. Complex shapes including inward taper region 58, 60 and raised portion 84 of base 52 are readily achieved by way of this process; indeed other stretch molding processes are likewise possible within the spirit and scope of the present invention. In addition, the rim may be locally thickened or a flange provided so that a lid may be more readily attached to a surface with some radial extent.
Rigidity
Commercially available plastic cups are typically made by injection-molding and/or thermoforming, neither of which techniques induce biaxial orientation. In order to characterize Rigidity, the force required to deflect the cup sidewall at ⅔ of the cup height is measured. This measurement is convenient because it is the location on the cup that the majority of people will grip. To assess Rigidity, an empty (dry) cup is restrained by V-blocks at its base, preferably having a weight placed in the bottom of the cup for stability. A movable probe and a stationary probe are positioned on the surface of the cup in opposed positions across the cup sidewall at ⅔ of the cup's height. The cup is then compressed between the probes and the force required for an inward deflection of specified distance of the sidewall is recorded in lb_f. This value is referred to herein as the “Rigidity” of the cup. Preferably, the Rigidity is measured at 75° F. and 50% relative humidity, the features of the test including securing the base of the cup, the height of the cup at which the deflection is measured, the deflection displacement and the force required to cause the deflection. Unless otherwise indicated below, the force required for a ¼ inch deflection at ⅔ cup height is reported as the Rigidity. For comparative purposes and to further characterize the cups of the invention, Rigidity at 1 inch sidewall deflection is sometimes used; in such instances, it is made clear that Rigidity at a 1 inch sidewall inward deflection is referred to. In the event peak force occurs before the specified deflection, peak force is used.
The Rigidity is preferably determined using a JS-1 Rigidity tester modified with a Chantillon Gauge. The Chantillon Gauge is available from:

- Chatillon
- Force Measurements Division
- P.O. Box 35668
- Greensboro, N.C. 27425-5668

919-668-0841 FAX 919-668-2746.
The test method was developed by:

- Georgia-Pacific Corporation
- Neenah Technical Center
- 1915 Marathon Avenue
- Neenah, Wis. 54956
- 920-729-8415, Test Method TM-4671-OM

As noted above, available cups are usually produced by thermoforming or by injection-molding-neither of which techniques induce biaxial orientation into the product. The Table 2 below shows Rigidity data for two commercially thermoformed 20-oz. PET cups and for a 22-oz. stretch blow-molded cup. Note that the Rigidity is much higher for the stretch blow-molded cup. Normally the stretch blow-molding process that is used for bottle making uses an optimized preform design in order to maximize the physical properties of the bottle produced. The preform used in this case was an off-the-shelf 2-liter bottle preform that was not specifically designed to produce the 22-oz. cup characterized in the table.

TABLE 2


Cup Rigidity

				Dry Rigidity
		Average		(lb_f/¼ in.
	Manufacturing	Weight	Volume	Deflection at
Sample	Method	(g)	(oz.)	⅔ height)

PET Cup A	Thermoformed	19.886	20 oz.	0.744
PET Cup B	Thermoformed	19.03	20 oz.	0.827
Blow-Molded PET	Stretch Blow-	22.53	22 oz.	1.430
Prototype*	Molded

*Not optimized for weight distribution or preform design, made by invention method

Relative Cup Rigidity

An equation to describe the Rigidity as a function of its strength to weight ratio is as follows: $Relative Cup Rigidity = (Rigidity) \times \frac{(Cup Volume)}{(Cup Weight)}$
where,
Rigidity is the force in pounds required to deflect the sidewall of the cup ¼ inch (usually) at ⅔ height,
Volume is in fluid-oz., and
Cup weight is in grams.

Below in Table 3 are the Relative Cup Rigidities for the cups of Table 2.

TABLE 3


Relative Cup Rigidity of 20-Oz. Cups


Sample	Manufacturing Method	Average Weight (g)	Volume (oz.)	$(Rigidity) \times \frac{(Cup Volume)}{(Cup Weight)} ({lb}_{f} fluid - oz . / gram)$

PET Cup A	Thermoformed	19.886	20-oz.	0.782
PET Cup B	Thermoformed	19.03	20-oz.	0.832
Blow-Molded	Stretch Blow-	22.53	22-oz.	1.396
Prototype of	Molded
Invention

Relative Cup Rigidity parameter is a universal way of comparing and organizing data on the Rigidity of PET cups manufactured by different methods such as thermoforming, injection-molding, or IBM to those made by stretch blow-molding without regard to structural features or composition. Broadly speaking for all cups made of PET, whether injection molded, thermoformed, injection blow-molded, or injection stretch blow-molded, our data indicates that: (i) Relative Cup Rigidities of less than 0.6 are characteristic of cups with unoriented sidewall material: (ii) Cups with sidewall material with low orientation have Relative Cup Rigidities between 0.61 and 0.95: (iii) Somewhat oriented, design fortified or injection molded cups have Relative Cup Rigidities between 0.96 and 1.25; and (iv) Biaxially oriented PET cups, such as those made by a two-step injection stretch blow-molding process have relative Rigidities of at least 1.26 or often greater than 1.35.

Less than 0.60 Unoriented

0.61 to 0.95 Low Orientation

0.96 to 1.25 Somewhat Oriented or Fortified

Greater than 1.26 Biaxially Oriented
The Relative Cup Rigidity parameter, while seemingly simple, factors in orientation gains in Rigidity from tensile strength, flexural modulus, and crystallinity that are achieved at low product weights and high surface areas, as measured by the weight of the cup in grams and the liquid volume held by the cup in fluid oz. The parameter provides an easy way to rank the efficiency of a material, process, and/or design to yield stiffness per unit weight and surface area. The volume factors in how the weight of the cup is distributed—accounting for wall thickness and added structural features. The Relative Cup Rigidity parameter is intended to provide a method for comparing lightweight cups of different shapes, sizes, and structural features. The method is dependent on the ability to deflect the sidewall ¼ inch at ⅔ of the cup height.

A series of commercially available and experimental cups were evaluated for Relative Cup Rigidity. Results appear below.

TABLE 4


Selected Relative Cup Rigidities

							Relative
					Weight/		Cup
			Cup	Cup	Volume		Rigidity
			Volume	Weight	Ratio	Rigidity	(lb_f-fluid
Sample	Material	Method	(oz.)	(grams)	(g/oz.)	(lb_f)	oz./gram)

C -Red	PS/HIPS	Thermoformed		16	11.82	0.74	0.688	0.931
Multilayer
D -	PS/HIPS	Thermoformed		16	13.51	0.84	0.840	0.995
Red
Multilayer
E	PS	IBM*	13.6	18.82	1.38	2.18	1.575
F	PS	IBM*	9.0	13.16	1.46	1.88	1.286
G	PET	IBM*	13.6	24.93	1.83	2.03	1.107
H	White	Injection		32	36.4	1.14	1.16	1.019
	HDPE	Molded
I	White	Injection		44	49.4	1.12	1.23	1.095
	HDPE	Molded
J	PET	Stretch Blow-	14.2	18.62	1.31	1.19	0.908
		Molded (one
		Step)**
K		Thermoformed		32	28.01	0.875	0.917	1.048
L	PET	Thermoformed		16	17.58	1.10	0.672	0.612
M	PET	Thermoformed		16	15.5	0.97	0.552	0.570
N	PS/K	IBM*	20	17.91	0.86	0.687	0.767
	resin
O	White	Injection-	32	36.6	1.14	1.00	0.874
	HDPE	molding

*Experimental tumbler; injection blow-molded without axial expansion
**Experimental Cup; not optimized

Relative Cup Rigidity of the inventive tumblers as compared with other cups is even more striking at 1 inch deflection as is seen, for example, by way of comparison with U.S. Pat. No. 6,554,154, to Chauhan et al. The test procedure of the '154 patent is detailed in Col. 5 thereof and is essentially the test procedure detailed above for measuring Rigidity described above except that the cups are placed on their sides and the force for a 1 inch deflection at ⅔ of the cup height is measured. For purposes of comparison, the above procedure for measuring Rigidity was followed for the cups of the invention (and others enumerated below) except the force required for 1 inch deflection at ⅔ cup height is recorded.

Table 5 below compares the data of Table 1 of the '154 patent for 16 oz. cups with Rigidity data (1 inch deflection) obtained with a nominal 22 oz. (26.4 oz.) cup of the present invention.

TABLE 5


Comparison of Relative Cup Rigidity at 1 Inch Deflection

		Mean
		Cup				Relative
	Mean	Force at 1	Rigidity			Cup
	Cup	inch	(lb_f) at 1	Vol-		Rigidity
	Weight	deflection	inch	ume	Weight	at 1 inch
Design	(oz.)	(oz.)	Deflection	(oz.)	(grams)	Deflection

U.S.	0.35960	10.210	0.638	16	10.195	1.001
Pat. No.
6,554,154
“Old”
U.S.	0.33433	9.994	0.625	16	9.478	1.055
Pat. No.
6,554,154
“New”
Stretch	—	—	5.227 (at	26.4	24.969	5.527
Blow-			1 inch)
Molded
Cup of
Invention
(PET)

Thus, it is seen that the cups of the invention are over five hundred % (500%) more rigid than cups of the '154 patent at 1 inch deflection on a Relative Cup Rigidity basis. Similar differences are seen with respect to other commercially available cups. Rigidity data (lb_f) appears in Table 6.

TABLE 6


Rigidity Values*

	Load	Load	Load	Load
	at .25	at .5	at .75	at 1.0
	inch	inch	inch	inch
	dflc	dflc	dflc	dflc
Sample	(lb_f)	(lb_f)	(lb_f)	(lb_f)

Nominal 22 oz.	1.690	3.114	4.036	5.227
Stretch
Blow-Molded
PET tumbler
16 oz.	0.789	1.593	2.260	2.722
Thermoformed
PET

16 oz.	0.669	1.373	2.038	2.999
Thermoformed
PET

32 oz.	0.730	1.472	2.284	3.153
Injection-
Molded (PP)

*Rigidity Value at 1 inch sidewall deflection

It is seen in Table 6 that a tumbler of the invention typically exhibits Relative Cup Rigidity values at 1 inch deflection at least about 65% greater than the other cups tested.
Rigidity Index
The Relative Cup Rigidity parameter may also be modified so as to index the Rigidity of cups of different polymer compositions to biaxially oriented PET cups by normalizing the data to PET. This is accomplished by multiplying the Relative Cup Rigidity by the ratio of the densities of the polymer to that of PET. Thus, a polystyrene cup may be indexed against a PET cup by multiplying the Relative Cup Rigidity by 1.05/1.33. Table 7 lists typical blow-moldable polymers and their densities. The Rigidity Index thus calculated allows one to compare various cups whether thermoformed, injection-molded, 1-step stretch blow-molded, and IBM (injection blow-molded as described in the '543 patent noted above) cups regardless of their design or material of construction, see Table 9. Furthermore, when cup Rigidity is measurable by sidewall deflection, the normalized parameter also extends to filled or reinforced materials such as calcium carbonate-filled polypropylene and to PP nanocomposites. See Table 10. $Rigidity Index \equiv (Rigidity) \times \frac{(Cup Volume)}{(Cup Weight)} \times \frac{(Density of Resin)}{(Density of PET)}$ $(units : {lb}_{f} fluid - oz . / gram)$
where,
Rigidity is the force in pounds required to deflect the sidewall of the cup ¼ inch at ⅔ height,
Cup Volume is in fluid oz.,
Cup Weight is in grams,
Density of Resin is the specific gravity of the base resin disregarding the effects of fillers or additives, and

Density of PET is the specific gravity of PET, which is taken as 1.33.

TABLE 7


Densities of Blow-Moldable Resins

			Factor to
Polymer	Grade	Density	Index Data to PET

PET	Kosa 2201	1.39	1.0451
PET	Eastapak 9921	1.33	1.0000
PS	Styron 685D	1.04	0.7820
PP	Exxon PP 9574 E6	0.91	0.6842
HDPE	Exxon HYA-301	0.954	0.7173
PC	Dow Calibre 200-3	1.20	0.9022
SAN	Tyril 880B	1.08	0.8120
K-Resin	Chevron-Phillips KR03	1.01	0.7594
HIPS	Atofina 825	1.05	0.7895

The stretch blow-molded cups of this invention highlight the differentiating aspects of these cups compared to the various types of cups on the market today. The 22-oz. reverse taper glass shape was used to demonstrate that reverse taper designs with sidewall embossed logos are possible with crystal clear, rigid, lightweight, indestructible characteristics. Design options make it more possible than ever to link Brand identification with cup shape at competitive prices.
Relative Cup Rigidity and Rigidity Index data on fortified brims, made by the top curl method and the can seamer method, are shown in Table 8. Note that without the advantage of process optimization of preform design and weight to volume ratios, the Rigidities of stretch blow-molded cups made from typical 2-liter bottle preforms are dramatically higher than cups made by other methods—up to 60% higher than the best thermoformed cups and 90-140% higher than typical cups. An experiment was performed by cutting stretch blow-molded PET bottles in two places—3½ inches from the base and 6½ inches from the base. The Relative Rigidities measured on the bottle samples were 0.87 for the 3½ inch sample and 0.79 for the 6½ inch sample. The Relative Rigidities of these samples are low for biaxially oriented PET materials because they did not have brims. Typically a brim can contribute up to 80% of the Rigidity of a thin-walled cup as compared to a similar cup without a brim.

There appears in Tables 9 and 10 comparisons of Rigidity Indices for cups of the invention and various other products.

TABLE 8


Rigidities of PET Cups

		Cup	Cup	Cup	Relative	Rig-
	Mate-	Weight	Volume	Rigidity	Cup	idity
Description	rial	(grams)	(oz.)	(pounds)	Rigidity	Index

22-oz. Reverse	PET	24.969	26.4	1.360	1.438	1.438
Taper Stretch
Blow-Molded
Brim Curled by
Can Seamer
22-oz. Reverse	PET	26.561	27.1	1.781	1.817	1.817
Taper Stretch
Blow-Molded
Brim Curled by
Top Curl Tooling
Structural Ledge
Thermoformed
12-14 oz.	PET	14.923	14	1.209	1.13	1.13
16 oz.		16.311	16	0.844	0.83	0.83
20 oz.		18.420	20	1.045	1.13	1.13
24 oz.		21.575	24	0.950	1.06	1.06
Thermoformed
12-14 oz.	PET	12.920	14.2	0.620	0.68	0.68
16 oz.		15.933	16	0.681	0.68	0.68
20 oz.		20.357	20	0.776	0.76	0.76
24 oz.		19.000	24	0.646	0.82	0.82
32 oz.		28.103	32	0.789	0.90	0.90
Thermoformed
16 oz.	PET	15.764	18.3	0.516	0.60	0.60
Thermoformed
16 oz.	PET	16.249	18.3	0.662	0.74	0.74
IBM (Injection
Blow-Molded)
14 oz. Cut	PET	25.105	14	1.960	1.093	1.093
Crystal
Design

14 oz. Cut		24.952	14	2.034	1.141	1.141
Crystal Design
IBM (Injection
Blow-Molded)
16 oz.	PET	24.097	16	0.850	0.564	0.56
One Step Stretch
Blow-Molded
14 oz. Cut	PET	20.638	13.9	0.916	0.62	0.62
Crystal

TABLE 9


Rigidities of Cups Made of Different Materials by Various Processes

			Cup	Cup	Relative
		Cup Weight	Volume	Rigidity	Cup	Rigidity
Description	Material	(grams)	(oz.)	(pounds)	Rigidity	Index

22-oz. Reverse	PET	24.969	26.4	1.360	1.438	1.438
Taper Stretch
Blow-Molded
Brim Curled by
Can Seamer
22-oz. Reverse	PET	26.561	27.1	1.781	1.817	1.817
Taper Stretch
Blow-Molded
Brim Curled by
Top Curl Tooling
Structural Ledge
16 oz.	Thermoformed	12.983	17.6	0.598	0.811	0.63
	Clear PS
16 oz	Thermoformed	14.931	18.3	0.617	0.756	0.59
	Clear/Colored
	PS

14 oz. - Swirl	IBM	17.272	13.9	1.545	1.243	0.97
Shape	Clear PS
14 oz. - Low		14.807	14.1	0.853	0.812	0.64
Faceted Shape
14 oz. - Cut		17.244	13.7	1.513	1.202	0.94
Crystal Design
Red Multilayer	Thermoformed	10.324	16.1	0.672	1.048	0.82
16 oz.	PS/HIPS
Blue Multilayer	Thermoformed	13.881	18.3	0.764	1.049	0.82
16 oz.	PS/HIPS
Red Multilayer	Thermoformed	11.332	18.6	0.544	0.892	0.70
16 oz.	PS/HIPS
Multilayer	Thermoformed	14.143	17.8	0.977	1.230	0.97
16 oz.	PS/HIPS
16 oz.	Thermoformed	9.282	15.9	0.488	0.836	0.65
	Opaque PS
16 oz.	Thermoformed	9.843	16.2	0.585	0.963	0.76
	Opaque PS
16 oz.	Thermoformed	9.903	16.1	0.400	0.650	0.51
	Opaque PS
16 oz.	Thermoformed	11.191	17.6	0.495	0.778	0.61
	White PS
32 oz.	Thermoformed	26.126	32.7	1.273	1.593	1.25
	HIPS/PS
32 oz.	Thermoformed	28.830	31.9	1.266	1.401	1.10
	White
	HIPS/PS
32 oz.	Thermoformed	29.290	32.6	0.971	1.081	0.85
	White
	HIPS/PS
32 oz.	Injection	36.533	31.8	1.059	0.922	0.62
	Molded White
	PP

32 oz.	Injection	35.483	32.6	0.748	0.687	0.47
	Molded
	Georgia-
	Green PP
22 oz.	Injection	32.881	25.2	1.350	1.035	0.70
	Molded
	Colored PP
White HDPE	Injection	36.567	32	1.001	0.876	0.62
32 oz.	Molded
	White
	HDPE

TABLE 10


Rigidities of Mineral-Filled Injection Molded Cups are Compared to Stretch
Blow-Molded Cups

22-oz. Reverse	PET	24.969	26.4	1.360	1.438	1.438
Taper Stretch
Blow-Molded
Brim Curled by
Can Seamer
22-oz. Reverse	PET	26.561	27.1	1.781	1.817	1.817
Taper Stretch
Blow-Molded
Brim Curled by
Top Curl Tooling
Structural Ledge
44-oz. Car Cup
100% Solvay	Injection	47.422	44	1.401	1.300	0.880
1801 PP
90% PP/10%	Molded	50.497		1.621	1.412	0.956
CaCO ₃
80% PP/20%	PP	54.290		1.798	1.457	0.986
CaCO ₃
70% PP/30%		59.364		2.070	1.534	1.038
CaCO₃
44-oz. Car Cup
100% PP	Injection	47.310	44	1.704	1.584	1.078
97% PP/3%	Molded	48.392		1.810	1.646	1.114
Nanoclay
94% PP/6%	PP	49.217		2.029	1.814	1.227
Nanoclay
44-oz. Car Cup -	Injection	48.751	44	0.809	0.730	0.519
HDPE	Molded
	HDPE

From the foregoing data, it is seen the cups of the invention exhibit significantly higher Rigidity Index values than one seen with other disposable cups. The observed values may be summarized as set forth in Table 11.

TABLE 11


Rigidity Index Summary

	Observed Rigidity Index Range,
Cup Type	lb_ffluid oz./gram

Stretch Blow-Molded Cups of	1.4-1.8
Invention
Thermoformed PET Cups	0.6-1.1
IBM PET	0.55-1.15
Thermoformed PS	0.5-1.1
IBM PS	0.6-1
Injection-Molded PP/HDPE	0.5-0.7
(unfilled)
Injection Molded PP/HDPE (filled)	0.5-1.2

The differences in observed Rigidity Index Values are perhaps better appreciated by reference to FIG. 1, wherein the observed ranges for the various cups are presented.
Crystallinity
Samples from the sidewall of Thermoformed Cup A, Thermoformed Cup B, and the Blow-Molded prototype of the invention were taken at the top of the sidewall (1 inch down), the middle of the sidewall and the bottom of the sidewall (1 inch up) and in some cases from the bottom of the cups using the following procedure.
Exemplars were cut from either #1 or #2 cork borers and placed in pre-weighed DSC pans that had known amounts of Dow-Corning 340 silicone heat sink compound (zinc oxide and polydimethylsiloxane). The heat sink compound improves thermal conductivity so that good quality first-heating DSC thermal data can be obtained. Known amounts of heat sink compound were also placed on top of the PET exemplars prior to the lids being clamped onto the pans.
For DSC experiments, samples were taken through heat/cool/heat regimens at heating and cooling rates of 10° C. per minute. The DSC instrument was calibrated with an indium metal standard.
Any suitable commercially available machine may be used such as a Perkin Elmer® Pyris® 6 DSC. The instrument is operated in the heating mode method. Data and results appear in Table 12 below wherein % crystallinity is calculated as follows: $% Crystallinity = \frac{Δ H_{melt} - Δ H_{cc}}{Δ H°} \times 100 %$
where ΔH°=140.1 J/g for PET

- ΔH_melt=measured heat of melting
- ΔH_ccmeasured heat of cold crystallization

Reference: DSC as Problem Solving Tool: Measurement of percent Crystallinity of Thermoplastics, W. J. Sichina, International Marketing Manager, Perkin Elmer® Instruments.

TABLE 12


Thermal Properties of Poly(ethylene terephthalate) Samples
Determined by DSC Heating Mode Method

Heat Sink

Cold

Sample

Cmpd Weight

Glass Transition

Crystallization

Melting

Weight

Bottom

Top

T_onset

T_mid

T_end

ΔCp

T_peak

ΔH_cc

T_onset

T_peak

ΔH_melt

Crystallinity

Sample

(mg)

(° C.)

(J/g° C.)

(° C.)

(J/g)

(° C.)

(J/g)

(%)

(1) PET Thermoformed Cup B
(20-oz.)
Sidewall Top (One inch down)	3.82	1.76	3.42
First Heating				44	61	—	0.12	142	−3.96	235	241	43.84	28
Second Heating				—	77	80	0.24	150	−5.43	241	246	32.55	19
Sidewall Middle	4.61	3.88	7.66
First Heating				65	68	70	0.12	102	−4.49	232	246	40.84	26
Second Heating				—	78	86	0.18	152	−5.21	238	248	38.86	24
Sidewall Bottom (One-inch up)	5.69	1.66	3.45
First Heating				73	74	—	0.31	118	−22.74	231	246	36.81	10
Second Heating				—	78	—	0.17	147	−5.82	237	249	41.80	26
Bottom of Cup	8.23	1.92	3.31
First Heating				65	67	69	0.35	127	−26.09	231	246	36.74	8
Second Heating				75	80	85	0.14	159	−6.43	235	247	35.83	21
(2) PET Thermoformed Cup A
(20-oz.)
Sidewall Top (One inch down)	5.74	5.95	3.17
First Heating				—	67	74	0.45	127	−27.09	233	246	38.56	8
Second Heating				78	80	82	0.17	148	−5.21	238	249	41.58	26
Sidewall Middle	6.79	1.86	2.08
First Heating				70	72	—	0.23	128	−28.19	235	247	39.18	8
Second Heating				74	78	81	0.11	152	−4.30	237	249	44.67	29
Sidewall Bottom (One-inch up)	5.34	2.46	4.64
First Heating				69	71	74	0.40	128	−28.53	233	247	38.56	7
Second Heating				68	78	90	0.20	145	−5.76	238	249	41.36	25
Bottom of Cup	9.43	1.46	2.84
First Heating				—	67	75	0.38	129	−30.95	232	247	40.06	7
Second Heating				73	79	—	0.15	146	−3.66	238	249	42.23	28
(3 Prototype
Sidewall Top (One inch down)	5.99	3.52	1.10
First Heating				46	61	—	0.10	92	−2.70	239	247	39.64	26
Second Heating				76	81	85	0.18	147	−4.85	232	246	31.94	19
Sidewall Middle	10.89	2.00	4.59
First Heating				57	59	66	0.07	97	−4.41	236	248	41.12	26
Second Heating				72	80	89	0.14	156	−5.16	238	251	42.84	27
Sidewall Bottom (One-inch up)	11.17	2.05	4.01
First Heating				61	63	67	0.05	106	−2.90	238	248	43.83	29
Second Heating				77	82	88	0.16	137	−1.14	234	248	35.34	24

The thicknesses of the thermoformed cups was also measured and samples of the blow-molded prototype tumbler were cold stretched in room temperature Instron® Tests and then evaluated further for crystallinity changes. Results appear in Table 13 for cold-stretched samples vs. unstretched samples.

TABLE 13


Effect of Cold-Stretch on Crystallinity - Blow-molded Prototype

Heat Sink

Cold

Sample

Cmpd Weight

Glass Transition

Crystallization

Melting

Weight

Bottom

Top

T_onset

T_mid

T_end

ΔCp

T_peak

ΔH_cc

T_onset

T_peak

ΔH_melt

Crystallinity

Sample

(mg)

(° C.)

(J/g° C.)

(° C.)

(J/g)

(° C.)

(J/g)

(%)

Dog-Bone CD Non-Stretch Area	9.36	2.99	3.31
First Heating				—	66	69	0.07	98	−3.01	226	247	41.12	27
Second Heating				—	81	—	0.17	155	−6.91	237	250	39.01	23
Dog-Bone CD Stretch Area	8.02	3.09	7.92
First Heating				—	—	—	—	100	−3.01	241	239	48.31	32
Second Heating				—	81	87	0.18	137	−1.59	233	237	32.78	22
Dog-Bone MD Non-Stretch Area	10.02	2.99	3.31
First Heating				—	68	—	0.06	107	−5.20	219	247	39.64	25
Second Heating				—	80	84	0.12	142	−2.09	239	250	40.97	28
Dog-Bone MD Stretch Area	9.49	1.53	12.49
First Heating				—	65	76	0.13	88	−7.45	244	250	59.67	37
Second Heating				78	82	85	0.16	146	−5.41	233	248	32.58	19

% Crystallinity = (ΔH_melt− ΔH_cc/ΔH°) × (100%)

Results of the foregoing tests are further summarized in Tables 14, 15 and 16.

TABLE 14


Thicknesses of Cups at Four Positions

PET Thickness (mils)

	Thermoformed	Thermoformed
Position Measured	Cup B	Cup A

Sidewall Top (One-inch down)	8.5	15.5
Sidewall Middle	10.3	16.6
Sidewall Bottom (One-inch up)	15.0	12.3
Bottom of Cup	42.5	33.0

Weights of a typical cup are: Thermoformed Cup B 19.00 g and Thermoformed Cup A 19.65 g

TABLE 15


% Crystallinities of “As Received” PET Samples
(First Heating DSC Data)

Crystallinities (%)

			Stretch
	Thermoformed	Thermoformed	Blow-
	Cup B	Cup A	Molded
Position Assayed	20-oz. Cup	20-oz. Cup	Prototype

Sidewall Top	28	8	26
(One-inch down)
Sidewall Middle	26	8	26
Sidewall Bottom	10	7	29
(One-inch up)
Bottom of Cup	8	7	—

TABLE 16


MD and CD Films From Stretch-Blow-Molded
Prototype Cups Showing the Effect That Stretching
(at Room temperature) Has on % Crystallinities

Crystallinities (%)

“Dog-Bone” Sample	Non-Stretched	Stretched

MD of Stretch Blow-Molded Prototype Cup	25	37
CD of Stretch Blow-Molded Prototype Cup	27	32

It will be appreciated from the foregoing that the stretch blow-molded cups of the invention exhibited high levels of relatively uniform crystallinity at all levels of the sidewall whereas the thermoformed cups did not. Moreover, room temperature stretching experiments indicate that further crystallinity gains can be realized by optimizing preform design. Thermoformed cup B had relatively elevated levels of crystallinity in its upper portion while thermoformed cup A was more uniform in terms of thickness and crystallinity; albeit at relatively low levels of crystallinity.
While the invention has been described in connection with its numerous features and improvements, modifications to specific examples given within the spirit and scope of the present invention will be readily apparent to those of skill in the art.

Claims

1) A method of making a blow-molded tumbler comprising:

(a) injection-molding a preform provided with a neck portion, a body portion and a bottom portion;

(b) stretch blow-molding the preform to form a first intermediate article therefrom wherein the preform is expanded radially as well as axially,

the first intermediate article being characterized by having a neck portion corresponding to the neck portion of the preform, a transition portion adjacent the neck portion of the first intermediate article and a tumbler portion adjacent the transition portion thereof, the tumbler portion of the first intermediate article being further characterized by having a base formed from the bottom portion of the preform and a sidewall formed from the body portion of the preform;

(c) severing the tumbler portion of the first intermediate article from its transition portion to form a second intermediate article having a base corresponding to the base of the first intermediate article and a sidewall extending upwardly therefrom to define an upper aperture, the aperture being generally larger in area than the base of the second intermediate article such that the tumbler portions are stackable; and

(d) fortifying the sidewall of the second intermediate article around the upper aperture to form the tumbler.

2. The method according to claim 1, further comprising the step of heating the preform after it is injection-molded and prior to blow-molding thereof.

3. The method according to claim 1, wherein said first intermediate article has a blow-up ratio of at least about 3 with respect to said preform.

4. The method according to claim 3, wherein said first intermediate article has a blow-up ratio of from about 7.5 to about 14 with respect to said preform.

5. The method according to claim 1, wherein said preform consists essentially of polyethylene terephthalate.

6. The method according to claim 5, wherein said polyethylene terephthalate has an intrinsic viscosity of from about 0.55 to about 1.05.

7. The method according to claim 1, wherein said preform has a weight of from about 10 grams to about 200 grams.

8. The method according to claim 1, wherein said tumbler has a contained volume of from about 7 to about 64 fluid oz.

9. The method according to claim 1, wherein said tumbler has an outward taper from its base to its upper aperture of from about 2 to about 12°.

10. The method according to claim 1, wherein the tumbler has a generally smooth sidewall adjacent to its fortified rim, free from thread features.

11. The method according to claim 1, wherein the fortified rim of the tumbler has a lateral thickness of from about 1.5 to about 10 times the thickness of the adjacent sidewall.

12. The method according to claim 1, wherein the tumbler sidewall has a wall caliper of generally from about 0.005 inches to about 0.1 inches.

13. The method according to claim 1, wherein the transition portion of the first intermediate article is provided with a circumferential groove adapted to receive a drive member for rotating the article during the step of severing the tumbler portion therefrom.

14. The method according to claim 1, wherein the tumbler comprises a polyethylene terephthalate polymer and lip curl is provided with a curling tool maintained at a temperature of from about 275° F. to about 350° F. around the upper aperture of the second intermediate article.

15. The method according to claim 1, wherein the step of fortifying the sidewall of the second intermediate article around the upper aperture comprises applying a rim-forming member to the sidewall around the upper aperture.

16. The method according to claim 15, wherein said rim-forming member comprises the same material as the tumbler.

17. The method according to claim 15, wherein said rim-forming member has U-shaped profile.

18. The method according to claim 33, wherein the preform is an unthreaded preform.

19. A tumbler prepared by the method of claim 1.

20. The tumbler of claim 1, wherein the tumbler is stackable.