Patent application title: Injection Stretch Blow Molded Polylactide Bottle and Process For Making Same
Pat Gruber (Longmont, CO, US)
Greg Roda (Broomfield, CO, US)
James Lunt (Wayzata, MN, US)
GREEN HARVEST TECHNOLOGIES, LLC
IPC8 Class: AB65D8500FI
Class name: Mechanical shaping or molding to form or reform shaped article shaping against forming surface (e.g., casting, die shaping, etc.) applying heat or pressure
Publication date: 2008-09-25
Patent application number: 20080230954
An injection stretch blow molding process for making containers from a
polylactic acid resin. In one aspect the process comprises molding the
polylactic acid resin into a perform, applying heat to the perform,
stretching and blowing the perform in axial and radial dimensions in
order to form a preliminary molded container, conditioning the molded
container pursuant to a first conditioning method, conditioning the
molded container pursuant to a second conditioning method, and stretching
and blowing the molded container in order to form a final molded
container. Relatively rigid bottles constructed in accordance with one or
more processes disclosed herein are also contemplated.
1. An injection stretch blow molding process for making containers from a
polylactic acid resin, comprising:molding the polylactic acid resin into
a preform;applying heat to the preform;stretching and blowing the perform
in axial and radial dimensions in order to form a preliminary molded
container;conditioning the molded container pursuant to a first
conditioning method;conditioning the molded container pursuant to a
second conditioning method; andstretching and blowing the molded
container in order to form a final molded container.
2. The injection stretch blow molding process of claim 1, wherein applying heat to the preform is performed substantially contemporaneously with molding the polylactic resin into a preform.
3. The injection stretch blow molding process of claim 1, wherein applying heat to the preform is performed subsequent to the molding of the preform.
4. The injection stretch blow molding process of claim 3, wherein applying heat to the preform is performed after the molded preform has cooled.
5. The injection stretch blow molding process of claim 1, wherein conditioning the molded container pursuant to a first conditioning method comprises raising the temperature and pressure of the molded container for a fixed period of time.
6. The injection stretch blow molding process of claim 1, wherein conditioning the molded container pursuant to a first conditioning method comprises direct contact heat setting.
7. The injection stretch blow molding process of claim 1, wherein conditioning the molded container pursuant to a first conditioning method comprises heat setting in an oven.
8. The injection stretch blow molding process of claim 1, wherein conditioning the molded container pursuant to a first conditioning method comprises raising the temperature of the molded container to a temperature above the glass transition temperature of the polylactic resin.
9. The injection stretch blow molding process of claim 1, wherein the first conditioning method and the second conditioning method are the same.
10. The injection stretch blow molding process of claim 1, wherein conditioning the molded container pursuant to a first conditioning method comprises raising the pressure of the molded container to a predefined pressure.
11. The injection stretch blow molding process of claim 1, wherein conditioning the molded container pursuant to a second conditioning method comprises raising the pressure of the molded container to a predefined pressure.
12. The injection stretch blow molding process of claim 1, wherein the polylactic resin is a copolymer having repeating L and D lactic acid units in which either the L or D units are the predominant repeating units and the predominant repeating units constitute 90 to 99.5% of the lactic acid repeating units.
13. The injection stretch blow molding process of claim 1, wherein the polylactic resin is a blend of copolymers wherein the predominant repeating units in the blend of copolymers constitute 90 to 99.5% of the lactic acid enantiomer repeating units.
14. The injection stretch blow molding process of claim 1, wherein 92 to 99% of the lactic acid enantiomer repeating units in the polylactic resin are of the predominant lactic acid enantiomer.
15. The injection stretch blow molding process of claim 1, wherein the polylactic resin includes at least one additive.
16. The injection stretch blow molding process of claim 15, wherein the additive is selected from the group consisting of a colorant and a thermal stabilizer.
17. A container formed from a polylactic acid-based resin through an injection stretch blow molding manufacturing process, the manufacturing process comprising:molding the polylactic acid resin into a preform;applying heat to the preform;stretching and blowing the perform in axial and radial dimensions in order to form a preliminary molded container;conditioning the molded container pursuant to a first conditioning method;conditioning the molded container pursuant to a second conditioning method; andstretching and blowing the molded container in order to form a final molded container.
18. The container of claim 17, wherein the average sidewall thickness of the container is greater than 40 mils.
19. The container of claim 17, wherein the average sidewall thickness of the container is greater than 60 mils.
20. An injection stretch blow molding process for making containers from a polylactic acid resin, comprising:molding the polylactic acid resin into a preform;raising the temperature of the preform to between 60.degree. C. and 80.degree. C.;stretching and blowing the perform in axial and radial dimensions in order to form a preliminary molded container;raising the temperature of the molded container to between 60.degree. C. and 100.degree. C.; andstretching and blowing the molded container in order to form a final molded container.
CROSS REFERENCE TO RELATED APPLICATION
This application is based upon, and claims priority to U.S. Provisional Patent Application No. 60/895,776, entitled Injection Stretch Blow Molded Polylactide Bottle and Process For Making Same, filed Mar. 20, 2007. The entirety of such provisional patent application, including all exhibits and appendices, are incorporated herein by reference.
FIELD OF THE INVENTION
Aspects of the present invention relate to the use of polylactide resin (PLA) in an injection stretch blow molding process to manufacture durable and relatively thick-walled containers suitable for repeated use. Other aspects of the present invention relate to PLA bottles produced using the processes described herein.
BACKGROUND OF THE INVENTION
Containers such as water bottles are often molded from thermoplastic resins such as polypropylene, PVC, PET and polycarbonate. Polycarbonate, in particular, is the material of choice for clear and durable thick walled drinking containers used for non-carbonated drinks. Such containers are often used by outdoor sporting enthusiasts and for baby bottles. The advantages of polycarbonate include high clarity, high impact resistance and non retention of odors. Drawbacks of polycarbonate include the fact that it is produced from non renewable resources and is thus difficult to dispose of at the end of its useful life. In addition, concerns have surfaced regarding the effects on human health due to potential leaching of residual monomers during contact with liquids. Environmental and resource conservation concerns have led to an increasing demand for substitute polymeric materials which are derived from renewable resources that will biodegrade in compost facilities as well as fit into the existing disposal/reuse recycling systems in use today.
Polylactide resins (also known as Polylactic acid or PLA) are available commercially. PLA is produced from annually renewable resources such as corn or sugar beet. In addition PLA is easily composted to produce carbon dioxide and water. There are no known health issues associated with PLA products in the marketplace today. For these reasons there is significant interest in replacing polycarbonate with PLA, particularly in bottle and container applications.
Previous attempts at using PLA to produce injection stretch blow molded (ISBM) bottles have focused exclusively on thin-walled single use products such as those used in short shelf life applications like still water, juice, oils and milk. U.S. Pat. No. 5,409,751, the details of which are incorporated into the present disclosure by reference, describes such a process. The process described in U.S. Pat. No. 5,409,751 involves first forming a preform, or "plug", which is hollow and has dimensions far smaller than that of the final container. The preform is molded into a container by inserting it into a mold, and stretching it both axially (i.e. along its length) and radially. The axial stretching is done mechanically by inserting a pusher rod into the preform and mechanically extending it towards the bottom of the mold. Radial stretching is accomplished by injecting a compressed gas into the plug, thereby forcing the resin outward to contact the interior surface of the mold. Typically, a preliminary radial stretch is preformed by injecting a first increment of gas. This makes room for the stretcher rod, which can then be inserted. The preform is then stretched and immediately afterward is blown with more gas to complete the blow molding operation.
ISBM processes are generally divided into two main types. The first is a one-step process, in which the preform is molded, conditioned, and then transferred to the stretch blow molding operation before the preform has cooled below its softening temperature. The second type of ISBM process is a two-step process in which the preform is prepared ahead of time and stored for later use. In the two-step process, the preform is reheated prior to the initiation of the stretch blow molding step. The two-step process has the advantage of faster cycle times, as the stretch blow molding step does not depend on the slower injection molding operation to be completed. However, the two-step process presents the problem of reheating the preform to the stretch blow molding temperature. This is usually done using infrared heating, which provides radiant energy to the outside of the preform. It is sometimes difficult to heat the preform uniformly using this technique and unless done carefully, a large temperature gradient can exist from the outside of the preform to the center. Conditions usually must be selected carefully to heat the interior of the preform to a suitable molding temperature without overheating the outside. The result is that the two-step process usually has a smaller operating window than the one-step process.
In the two-step process, the preform is generally heated to a temperature at which the preform becomes soft enough to be stretched and blown. This temperature is generally above the glass transition temperature (Tg) of the PLA resin. A preferred temperature is from about 70 to about 120° C. and a more preferred temperature is from about 80 to about 100° C. The transition temperature is dependent upon the specific PLA resin being used. In order to help obtain a more uniform temperature gradient across the preform, the preform may be maintained at the aforementioned temperatures for a short period to allow the temperature to equilibrate.
Mold temperatures in the two-step process are generally below the glass transition temperature of the PLA resin, such as from about 30 to about 60° C., especially from about 35 to about 55° C. Sections of the mold such as the base where a greater wall thickness is desired may be maintained at even lower temperatures, such as from about 0 to about 35° C., especially from about 5 to about 20° C.
In the one-step process, the preform from the injection molding process is transferred to the stretch blow molding step while the preform is still at a temperature at which the preform becomes soft enough to be stretched and blown, again preferably above the Tg of the resin, such as from about 80 to about 120° C., especially from about 80 to about 110° C. The preform may be held at that temperature for a short period prior to molding to allow it to equilibrate at that temperature. The mold temperature in the one-step process may be above or below the Tg of the PLA resin. In the so-called "cold mold" process, mold temperatures are similar to those used in the two-step process. In the "hot mold" process, the mold temperature is maintained somewhat above the Tg of the resin, such as from about 65 to about 100° C. In the "hot mold" process, the molded part may be held in the mold under pressure for a short period after the molding is completed to allow the resin to develop additional crystallinity and relax residual stresses in the amorphous phase (commonly referred to as heat setting). The heat setting tends to improve the dimensional stability and heat resistance of the molded container while still maintaining good clarity. Heat setting processes may also be used in the two-step process, but are used less often in that case because the heat setting process tends to increase cycle times.
Blowing gas pressures in either the one-step or two-step processes typically range from about 5 to about 50 bar (about 0.5 to about 5 MPa), such as from about 8 to about 45 bar (about 0.8 to about 4.5 MPa). It is common to use a lower pressure injection of gas in the preliminary radial stretch, followed by a higher pressure injection to complete the blowing process. ISBM processes can further be defined as either a single blow process, where the preform is stretched to its final shape in a single blowing process, or a double blow process, where the perform is first blown followed by a second blow process using the previously formed bottle.
Nalgene® is one of the registered trademarks of Nalge Nunc International, or its subsidiaries. One of Nalge's major products is a line of clear plastic drinking water bottles of various size marketed to outdoor enthusiasts. Produced from polycarbonate by an Injection Stretch Blow Molding Process (ISBM), the key properties of these bottles are high impact resistance and resistance to staining. In addition, they do not retain odors, are capable of withstanding sub-freezing to boiling temperatures, are dishwasher safe away from the heating element, and can withstand temperature ranges of 135° C./275° F. to -135° C./-211° F. These properties make the Nalge bottles, and others formed from a similar polycarbonate, appealing to consumers who need a durable and reusable bottle for various activities.
The polycarbonate material these bottles are formed from is an amorphous polymer with a glass transition temperature of approximately 148° C. The material has high toughness, transparency and very low moisture absorption as additional positive attributes for this market. However, these polycarbonate bottles have several negative attributes including that they are derived from non-renewable oil based resources, have high melt processing temperatures of approx 200C, and have a relatively high material cost.
In addition, since 1993, increasing health concerns have been raised over the extraction of bisphenol A into the water contained in polycarbonate bottles. See, Our Stolen Future at www.ourstolenfuture.org; The ecological footprint of Nalgene water bottles (2006) Deanna Thompson, Kyla Patterson, Elizabeth Whittaker, & Sally Haggerstone. Bisphenol A is also used in other resins such as epoxies and has been associated with chromosomal aberrations, thus raising questions about the safety of consumer products made with polycarbonate, especially when they are designed to contain food or water. The research on chromosome damage, by a team of Case Western Reserve scientists, found that bisphenol A leaching out of polycarbonate bottles used to provide water to mice caused a chromosomal error in cell division called aneuploidy. In humans, aneuploidy is one the largest causes of miscarriages and birth defects, including Down Syndrome. While the link to humans is not conclusive, the process of cell division in mice is very similar to that of humans, and scientists suspect that the causes of aneuploidy in humans should be similar if not identical. Another issue of concern is the environmental emissions involved in both the manufacture of the monomers and polymer (2). Thus there is a need to offer a replacement to these rigid, durable and reusable bottles that offers the same performance characteristics while eliminating the negative attributes associated with their use.
Polycarbonate bottles, such as the clear Nalgene® type found in many outdoor sporting goods retail stores, are typically made by one or more of the same injection stretch blow molding process known and described above.
Despite the foregoing, it has until now been difficult to produce relatively thick walled (e.g. >30 mil or 0.76 mm) PLA bottles that maintain their thermal stability and rigidity through these conventional ISBM processes. There is no indication that anyone has been successful to date in developing a process for rigid PLA bottles that utilizes the double blow ISBM technique. Furthermore, single blow PLA processes have not been successful at producing a reusable bottle that can maintain the rigidity and thermal stability necessary for such applications described above.
PLA products have high MVTR and high oxygen and carbon dioxide transmission rates which exclude PLA bottles from the longer life beverage/drinks bottle applications and carbonated soft drinks markets. However, the properties of PLA for the short shelf life, more durable non-carbonated market segment presently occupied by polycarbonate Nalgene®-type bottles, hold significant potential to meet the functional requirements of this market segment. In comparison to polycarbonate, PLA has superior oxygen and carbon dioxide permeability although, as already noted, the carbon dioxide permeability of both polymers makes both unsuitable for the carbonated drinks market Laboratory testing of PLA single use bottles and prototype durable thick walled bottles has shown that PLA bottles survived the industry drop test of 3 meters onto concrete and a 45 degree angle with the bottle full of water. Thus, it is contemplated that thick walled PLA bottles will also meet the market requirements for the more durable, transparent, refillable, non-carbonated market segment presently occupied by polycarbonate bottles. Aspects of the present invention also relate to the reusable containers produced in accordance with the manufacturing processes described below.
SUMMARY OF THE INVENTION
An injection stretch blow molding process for making containers from a polylactic acid resin. The process comprises molding the polylactic acid resin into a perform, applying heat to the perform, stretching and blowing the perform in axial and radial dimensions in order to form a preliminary molded container, and conditioning the molded container.
Another aspect of the present invention includes an injection stretch blow molding process for making containers from a polylactic acid resin. The process comprises molding the polylactic acid resin into a perform, applying heat to the perform, stretching and blowing the perform in axial and radial dimensions in order to form a preliminary molded container, conditioning the molded container pursuant to a first conditioning method, conditioning the molded container pursuant to a second conditioning method, and stretching and blowing the molded container in order to form a final molded container. Relatively rigid bottles constructed in accordance with one or more processes disclosed herein are also contemplated.
BRIEF DESCRIPTION OF THE DRAWINGS
Various objects and advantages and a more complete understanding of the present invention are apparent and more readily appreciated by reference to the following Detailed Description and to the appended claims when taken in conjunction with the accompanying Drawings wherein:
FIG. 1 is a schematic diagram/flow chart of a single blow ISBM process;
FIG. 2 is a schematic diagram/flow chart of a double-blow ISBM process; and
FIG. 3 is a drawing showing the details of a representative PLA bottle produced pursuant to one or more of the processes described herein.
Aspects of the present invention relate to ISBM manufacturing processes for producing relatively thick walled containers from a PLA resin wherein (1) the PLA is a copolymer having repeating L and D lactic acid units in which either the L or D units are the predominant repeating units and the predominant repeating units constitute 90 to 99.5% of the lactic acid repeating units; (2) the product of axial and radial stretch ratios is from about 3 to about 17.5; and (3) where the wall thickness of the final container is from about 30 to about 80 mils, although wall thicknesses greater than 80 mils are also contemplated in some embodiments.
Due to the environmental concerns associated with polycarbonate discussed above, for short shelf life outdoor sporting applications, transparent bottles meeting the performance requirements of this market segment could be produced from a renewable resource based polymer such as Polylactic acid (PLA). PLA polymers are already in the marketplace for single use, short shelf applications such as non carbonated water sold through retail stores. Because of their low wall thicknesses (10-12 mil), which leads to low durability, poor impact performance, and low temperature performance (130° F./55° C.), these single use products will not meet the demands of the outdoor multiple use sporting goods market. It has been shown in connection with aspects of the present invention that these issues can be overcome by the use of various heat-setting techniques and modifications to ISBM processes.
The ISBM process in accordance with aspects of the present invention can be either a one or two step process as described more fully below and can utilize either a single blow or a multiple blow process. While not specifically required, in preferred embodiments, a double blow process has been shown to yield desirable results. It should be noted that while some embodiments within the specification might be referred to as preferred, this language is not intended to limit the scope of the claims to these specific embodiments, unless specifically indicated in the specification and claims. The claims are meant to encompass the broadest interpretation that is consistent with the plain meaning of the terms as confirmed by the specification.
As described more fully below, the use of PLA resin within the processing guidelines and specific manufacturing specifications stated below and as set forth in the appended claims, allows for containers to be produced through an ISBM process that have controlled crystallinity, good clarity, good impact performance, and increased thermal stability over previously produced PLA containers.
In general, thick walled containers in accordance with aspects of the present invention are made using an injection stretch molding (ISBM) process. Such ISBM processes are well known, being described for example in U.S. Pat. No. 5,409,751, the details of which are incorporated into the present disclosure by reference in their entirety, and further described in FIG. 1. The generalized ISBM process 100 involves first forming a preform or "plug" at step 102 which is hollow and whose dimensions are a fraction of those of the final container. The perform geometry is specifically designed to produce a container of a determined geometry. The preform can be formed, conditioned, and transferred to the stretch blow molding operation before the preform is cooled below its softening temperature at step 104. This process is commonly referred to as a "one step" process since the perform is prepared and blown into a container in a single step, prior to the perform cooling.
In another well known process, the preform is allowed to cool below its softening point and can then be stored for use at a later time at step 103. The preform is then reheated to carry out the stretch blow molding process when needed at step 104. This process is commonly referred to as a "two-step" process. Conditioning step 106 may be carried out depending on the specific application. After any such conditioning, the finished bottled is ejected from the processing machine at step 108
The two step process is most often employed for the manufacture of thick walled durable containers such as the Nalgene-type bottles described above. The two-step process has the advantage of faster cycle times since the stretch molding process step does not depend on the slower preform injection molding process. Additionally, for the production of thick walled containers the preform temperature can be accurately controlled to allow even material distribution and stress distribution in the final part, thereby providing the required durability and robustness required.
In a double blow process, the following general steps are utilized. FIG. 2 describes such a process 200. First a preform is prepared at 202 and reheated and/or conditioned. Preferably, the preform is rotated during this process to ensure a consistent reheat. Next, during a primary blow-molding step 204 the reheated preforms are stretch blown in a primary stretch blow mold. Next, in a first conditioning step 206, heat setting or some other type conditioning is achieved. Heat setting can be performed through, for example, a direct contact procedure. Next, a second conditioning step 208 is applied, for example heat processing in an oven or other contained environment. Finally, the bottle undergoes a final blow-molding step 210 in which the bottle takes its final form prior to being ejected from the processing equipment 212. Various modifications to one or more of the above double-blow process are known in order to fine tune the resulting bottle. However, no one has attempted to use a double blow ISBM manufacturing process in order to create a relatively thick-walled and rigid PLA bottle in accordance with one or more aspects disclosed herein.
The controlled reheating of the preform and the subsequent stretch blow molding step are also highly dependent on the grade of PLA resin utilized. Typically, the three significant resin variables are: 1) molecular wt, 2) viscosity versus temperature, and 3) enantiomeric ratio (L to D ratio). All three variables must be carefully selected and controlled to enable a practical processing window for the manufacture of thick walled containers. The correct selection of the resin grade is also essential if high clarity is also required in the final part. Examples of enantiomeric ratio, extensional viscosity and molecular weight information can be found, for example, in PCT Patent Application publication No. WO2006/002409 assigned to NatureWorks LLC. The details of this reference are hereby incorporated into the present disclosure by reference in its entirety.
Mold temperatures in a two-step process are generally held below the glass transition temperature of the PLA resin, typically from about 30-60° centigrade and most preferably in the 35-55° centigrade range.
In order to obtain the required dimensional stability in the final container it may be necessary or preferable to include a "heat setting" step. In one example, the mold temperature may be raised to 65-100° C. and the molded part held under controlled pressure for a short period of time. This allows stress relief and increased crystallinity to develop while maintaining the clarity in the part.
The following represent various examples and processing results related to the use of one or more different types of ISBM processes to process a relatively think-walled container from PLA resin. As stated above, these examples are not meant to limit the scope of the claims but are provided as representative examples.
0.5 liter bottles were prepared from specific PLA resins in a two-step ISBM process as follows. Preforms having a weight of 100-180 gms were prepared via injection molding by heating the resin to a temperature of 200-220° and injecting the resin into a preform mold specifically designed for PLA and the final container dimensions. Such a perform design takes into account the different extensional viscosity properties of PLA compared to other polymers. The molding conditions were optimized to produce performs with even wall thickness, minimal part stress and clear parts free of haze. The preforms were cooled to room temperature before stretch blow molding in a separate step. Stretch blow molding was accomplished using a typical stretch blow molding machine used for PET or PC bottles at cycles of up to 2000 bottles/hour.
The PLA resins used were 1) a first copolymer of 96% L and 4% D having a relative number average molecular wt of above 100,000, and 2) a second copolymer of 98.4% L and 1.6% D having a relative molecular wt. of above 100,000. Alternately, the perform weight can be in the range of 100-180 gms. Alternatively, the above example may be performed via a one-step process, where the conditioning step is eliminated.
Overview--PLA bottles were produced at several blow molding conditions to determine the effects of heat set blow molding and the double blow molding process on the thermal stability of PLA bottles. The blow molding conditions used to produce bottles are summarized below.
1. Standard 45° F. mold temperature (to use as reference)
2. Double blow molding process (200° F. mold temperature for both passes)
3. 160° F. Mold setpoint temperature
4. 165° F. Mold setpoint temperature
5. 170° F. Mold setpoint temperature
6. 175° F. Mold setpoint temperature
7. 180° F. Mold setpoint temperature
8. 190° F. Mold setpoint temperature
9. 200° F. Mold setpoint temperature
10. 220° F. Mold setpoint temperature
11. 200° F. Mold setpoint temperature with 110° F. base temperature
Thermal Stability--Six (6) bottles, from sets 1-10 listed above, were tested for thermal stability at 150° F. The diameters, height and volume of each bottle were measured before placing the empty bottles in an oven at 150° F. for 24 hours. Once the bottles were removed from the oven and cooled to room temperature, they were re-measured. The difference of these measurements was reported as a percent change. If the bottles showed excessive shrinkage at the 150° F. storage temperature, the oven temperature was reduced in 10° F. increments for the storage until acceptable shrinkage was observed.
Color and Haze Testing--The color and haze of the bottle sidewall from 1 bottle of sets 1-10 was measured at the top and bottom of the panel of the bottle.
Crystallinity via DSC--The crystallinity in the center of the panel area of the bottle was measured for sets 1-10. The crystallinity was also be measured in the base of sets 2, 10, and 11. Finally, the crystallinity was measured in the finish for sets 2 and 10.
In this example, the effects of mold temperature and the use of a double blow process on PLA container thermal stability was investigated. Preforms were injection molded using NatureWorks 7032D PLA resin and a Colormatrix toner/reheat additive. Injection molding techniques were used to mold a 40 g PLA perform designed to blow mold into an 18 oz Boston round container. These preforms were then blow molded using a Sidel SBO 1/2 single cavity blow molding machine. Once conditions that produced an acceptable bottle were determined, bottles were produced at several blow mold temperatures for thermal stability testing. Approximately 50 bottles were produced using a 200° F. mold. These bottles were then taken and re-blown for thermal stability testing. Results showed that, in general, as the blow mold temperature set point increased, the thermal stability of the bottle also increased. Also, bottles that are double blown also displayed improved thermal stability.
Injection Molding--The PLA resins in the previous example were dried overnight at 176° F. to achieve a moisture level below 250 ppm prior to injection molding. Once dry, the appropriate amount of Colormatrix 80-740-2 reheat toner was added to an aluminized mylar bag, then purged with nitrogen and sealed. The aluminized Mylarbags were then placed on a tumbler for 10-15 minutes to allow an even distribution of material. The resin samples were injection molded on an Arburg 420M reciprocating screw injection molding machine using a 40 g preform tool designed to blow mold into a thick-walled 18 oz Boston round container. The following table summarizes the injection molding conditions used for this trial. Approximately 300 preforms were produced using these conditions.
TABLE-US-00001 7032D + Colormatrix Variable Description 80-740-2 Injection Molding Conditions Machine #6 Arburg 420 M Preform # PRE-5568 1 Preform Weight (g) 40.3 Relative Humidity 21% Dew Point (° F.) 53 Mold Temp (° F.) 60 Ambient Temp (° F.) 74 Dryer Temp (° F.) 175 Barrel Temperatures Feed (° C.) 215 Zone 2 (° C.) 216 Zone 3 (° C.) 215 Zone 4 (° C.) 216 Nozzle (° C.) 212 Injection Injection Pressure 1 (bar) 800 Injection Time (sec) 4.0 1st Injection Speed 12.0 (ccm/sec) 2nd Injection Speed 10.0 (ccm/sec) Holding Pressure Switch-Over Point (ccm) 8.0 1st Hold Pressure (bar) 250.0 2nd Hold Pressure (bar) 200.0 3rd Hold Pressure (bar) 100.0 1st Hold Pr. Time (sec) 2.0 2nd Hold Pr. Time (sec) 3.0 3rd Hold Pr. Time (sec) 2.0 Remain Cool Time (sec) 16.0 Dosage Circumf. Speed (m/min) 12.0 Back Pressure (bar) 25.0 Dosage Volume (ccm) 45.0 Meas. Dosage Time (sec) 5.1 Cushion (ccm) 7.4 Adjustment Data Cycle Time (sec) 33.1
Blow Molding--Preforms were then blown using a Sidel SBO1/2 blow molding machine. Conditions were optimized for the best section weights and overall consistency that could be achieved. Even material distribution throughout the sidewall of the container is addressed through preform design modifications.
Initially the blow mold set point temperature was 160° F. Approximately 10 bottles were produced at this condition. Next, the blow mold set point temperature was increased in 5-20° F. increments until acceptable bottles could not be produced. 10 bottles were collected at each blow molding interval and tested for color, crystallinity and thermal stability. Bottles were first blown under heat set conditions, increasing mold temperatures by 10° F. until an acceptable bottle could no longer be produced. The highest mold temperature that could be used to produce bottles was 220° F. One bottle from each of these blow molding conditions was placed into an oven overnight at 150° F. These bottles were visually inspected the following morning. Observation indicated that bottles that were blown using a 200° F. set point temperature appeared to shrink and deform the least.
On the second day of blow molding, the mold temperature of the base was increased in increments of 10° F. until the base of the bottle began to roll out. Once this temperature was determined, it was reduced 10° F. to produce 50 samples for the double blow process. These bottles were then passed through the blow molder oven in order to shrink the bottle and relax the existing stress in the bottle's sidewall. Since wall thickness of the bottles is thin compared to the preforms, less heat was required to reheat the bottles compared to the preforms. To achieve this, one of the oven banks was turned off and the blow molder's speed was increased. Blow molding conditions were further optimized to produce a double blown container with the best distribution that could be achieved.
The following table includes the conditions used to blow mold each condition. Note that the condition No. 11 was used to produce the first pass
TABLE-US-00002 Blow Molding Conditions 7032D + 7032D + CM 80- CM 80- Resin 7032 D 7032 D 7032 D 740-2 740-2 Speed (bph) 500 900 500 500 500 Overall 43 45 37 37 37 Oven Lamp Settings Zone 10 0 55 0 0 0 Zone 9 0 55 0 0 0 Zone 8 55 55 55 55 55 Zone 7 55 45 55 55 55 Zone 6 45 45 45 45 45 Zone 5 45 45 45 45 45 Zone 4 46 55 46 46 46 Zone 3 16 0 16 16 16 Zone 2 0 0 0 0 0 Zone 1 100 70 100 100 100 Low Blow Position (mm) 170 245 170 170 170 Low Pressure (bar) 10 6.5 10 10 10 High Blow Position 285 285 285 285 285 (mm) High Blow Pressure (bar) 40 30 40 40 40 Preblow Flow (bar) 1 1 1 1 1 Body Mold Temp (° F.) 45 110 160 165 170 Base Mold Temp. (° F.) 45 90 65 65 65 Preform Temp. (° C.) 78 82 76 76 75 Top Weight(g) 7.7 0 0 0 0 Panel Weight(g) 23.3 0 0 0 0 Base Weight(g) 9.2 0 0 0 0 Weight(g) 0 0 0 0 0 7032D + 7032D + 7032D + 7032D + 7032D + 7032D + CM CM 80- CM 80- CM 80- CM 80- CM 80- Resin 80-740-2 740-2 740-2 740-2 740-2 740-2 Speed (bph) 500 500 500 500 500 500 Overall 37 37 37 37 37 37 Oven Lamp Settings Zone 8 55 55 55 55 55 55 Zone 7 55 55 55 55 55 55 Zone 6 45 45 45 45 45 45 Zone 5 45 45 45 45 45 45 Zone 4 46 46 46 46 46 46 Zone 3 16 16 16 16 16 16 Zone 2 0 0 0 0 0 0 Zone 1 100 100 100 100 100 100 Low Blow Position 170 170 170 170 170 170 (mm) Low Pressure (bar) 10 10 10 10 10 10 High Blow Position 285 285 285 285 285 285 (mm) High Blow Pressure 40 40 40 40 40 40 (bar) Preblow Flow (bar) 1 1 1 1 1 1 Body Mold Temp 175 180 190 200 220 200 (° F.) Base Mold Temp. (° F.) 65 65 65 65 65 110 Preform Temp. (° C.) 75 75 75 75 75 75
Thermal Stability--Bottles from condition Nos. 1-10 were placed in a 150° F. oven for 24 hours and then measured for dimensional changes. Note that in these results, negative results represent shrinkage and positive results represent growth due to deformation.
TABLE-US-00003 Thermal Stability Results (Sets A1-A5) Variable Name Set A1 Set A2 Set A3 Set A4 Set A5 Mold Temperature (° F.) 200 45 Double 160 165 170 % Average -9.41% -8.48% -10.63% -10.43% -10.49% Height Change St Dev 0.97% 0.80% 0.54% 1.54% 0.93% % Neck Average 0.17% -0.62% -1.94% -1.89% -2.54% Change St Dev 0.77% 0.45% 0.55% 0.68% 0.48% % Average n/a 8.36% 7.36% 5.48% 6.16% Upper Label St Dev n/a 1.84% 2.49% 1.35% 2.14% Change % Average n/a -0.51% -1.28% -0.26% 1.11% Middle Label St Dev n/a 1.69% 3.58% 4.56% 1.78% Change % Average n/a 5.79% 4.75% 4.50% 7.14% Lower Label St Dev n/a 1.33% 1.32% 2.35% 1.21% Change
TABLE-US-00004 Thermal Stability Results (Sets A6-A10) Variable Name Set A6 Set A7 Set A8 Set A9 Set A10 Mold Temperature (° F.) 175 180 190 200 220 % Height Average -10.94% -8.86% -9.43% -8.45% -7.28% Change St Dev 1.20% 0.56% 1.14% 0.77% 0.38% % Neck Average -3.59% -1.97% -3.27% -2.54% -2.48% Change St Dev 0.29% 1.33% 0.43% 0.54% 0.26% % Upper Average 7.08% 4.87% 7.00% 7.28% 9.44% Label St Dev 1.14% 2.22% 1.42% 1.56% 1.30% Change % Middle Average -0.67% 0.93% 3.34% 3.87% 4.16% Label St Dev 3.34% 1.32% 0.84% 0.67% 0.62% Change % Lower Average 6.01% 3.24% 6.30% 6.34% 7.25% Label St Dev 2.41% 1.34% 0.85% 0.81% 1.38% Change
While all of the bottles were distorted after storage in the oven, as the mold temperature increased, there was a general trend of improvement in thermal stability. The double-blow process itself also helped with the thermal stability.
Color/Haze Results--The sidewall of 1 bottle from each of the blow molding conditions was measured for color and haze. Measurements were made in two locations of the panel, the upper and lower panel. In general, the amount of haze in the upper panel was greater than in the lower panel of the same condition, and as the mold set point temperature was increased the amount of haze increased.
DSC Results--Differential scanning calorimetry was performed on these bottles at a few different locations on the bottle to understand the effect that mold temperature has on the crystallinity of the bottles. As the mold set point temperature increases the ΔHc decreases, the ΔHc at 220° F. mold temperature and after double blowing. To understand the effect of base temperature on the base crystallinity a DSC was also run on the double blown bottles, bottles molded at 220° F. (65° F. base, used as reference), and bottles blown using a 110° F. base temperature were run. The ΔHc of the 110° F. was slightly lower than the 65° F. The ΔHf was similar for these two measurements. There was not a crystallization peak to measure for the double blown sample. To verify that the double blow process was not changing the thermal characteristics of the finish, DSCs were performed on the finish from a double blown bottle and the finish from a first pass bottle.
TABLE-US-00005 DSC Results Condition Location Tg ΔHc Tf ΔHf A1 - 45° F. Panel 63.2 5.336 165.6 23.1 A2 - 200° F. (Double) N/A N/A 164.6 22.7 A3 - 160° F. 60.6 5.847 164.1 22.56 A4 - 165° F. 59.65 4.232 164.9 23.4 A5 - 170° F. 61.75 4.434 165.4 24.18 A6 - 175° F. 60.07 2.632 165.01 23.14 A7 - 180° F. 62.89 3.095 165.07 24.56 A8 - 190° F. 60.02 1.699 164.6 24.25 A9 - 200° F. 60.65 0.907 165.01 23.8 A10 - 220° F. 60.61 N/A 164.81 24.79 A2 - 200° F. (Double) Base N/A N/A 165.57 22.41 A10 - 220° F. 60 16.2 167.51 20.46 A11 - 200° F. (110° F. 57.8 14.61 167.04 20.01 Base) A2 - 200° F. (Double) Finish 58.62 11.52 166.6 20.51 A10 - 220° F. 59.65 12.51 166.74 19.26
The thermal stability of the containers improves as the blow mold temperature increases and if the bottles are double blown. The main shrinkage is in the base of the bottles and the thinner portions of the sidewall, however there are small amounts of deformation in the thicker portions of the sidewall. The haze and DSC results are consistent with increasing crystallinity with increasing blow mold temperature.
Overview--The focus of this bottle prototyping trial was to determine whether the heat resistance of oriented, thick-walled PLA containers can be improved through the heat setting process. A Boston round container mold with heat setting capability was used to produce bottles. The blow mold cavity for the Boston round container will be heated to allow the PLA to anneal during the blow molding step, however, the finish and base areas remain amorphous due to the design of the blow molding and the need to maintain a cold finish area to prevent deformation. The bottles were evaluated for thermal stability, sidewall rigidity, haze and top load strength.
The feasibility of crystallizing the amorphous finish was also evaluated by placing the finish into a hot oven to crystallize that region. These preforms will then be blow molded under the optimized conditions determined with untreated preforms. Alternatives to this process is to include a bottle design that has a blow and trim feature allowing the finish area to be blown into the sidewall of the container.
Preform Design--A preform and tooling based on the target stretch ratios of 3-4 hoop stretch and >2 axial stretch ratio to produce a container thickness of 0.030'' was designed. This preform design allows for more orientation in the base area, which leads to improved drop impact performance.
Sampling--Preform samples were produced with two PLA resins, 7000D and 7032D, along with a reheat additive and possible pigment. A reheat additive was incorporated into all of the molded preforms to ensure that the reheat upon blow molding does not limit the process window. Once the preforms were molded, twenty-five preforms were treated to crystallize the threaded finish area while keeping the preform body cool to maintain its amorphous nature. These preforms were then held on spindles to avoid changing the internal dimensions of the preform so that they can be reheated in the blow molding process. Once successfully crystallized in the neck area, these preforms were blow molded under the optimized conditions. A 16 oz. Boston round style container with a 33 mm finish will be used in this blow molding trial. A champagne style base was designed and utilized with this mold in an attempt to orient the PLA material on the standing ring area where it will make contact during drop impact testing. This base push-up would also allow the material to be more fully distributed throughout the center of the base area as well. The bottle mold is heated through hot oil channels to heat set the PLA during the blow molding process. However, the finish and base areas are not heated during the blowing process and remain amorphous.
Forty preforms were available from the above procedure to setup and blow mold containers with a cold mold for thermal stability testing. Bottles were blown at 2 blow molding conditions for testing.
Blow Molding--NatureWorks 7032 preforms (See example 2 above) were blow molded using a Sidel SBO1/2 blow molding machine with mold temperatures set at 45° F. Initially the optimized blow molding conditions from the previous trial were attempted. At these conditions, the bottles were hazier in the neck area than they were in the previous trial and the material distribution was slightly different. The blow molding oven heating profile was then adjusted in an attempt to produce bottles with the same appearance and material distribution. During processing the sidewall thickness of several bottles were measured using a Magna-mike and it was determined that the sidewall thickness difference between these bottles and bottles made previously was 0.001'' or less. Bottles were produced for testing at two conditions; the table below summarizes the conditions used.
TABLE-US-00006 Resin 7032D + Toner 7032D + Toner Blow Molding Conditions Speed (bph) 500 500 Overall 37 37 Oven Lamp Settings Zone 8 50 50 Zone 7 50 50 Zone 6 40 45 Zone 5 60 45 Zone 4 55 40 Zone 3 20 25 Zone 2 20 20 Zone 1 97 100 Low Blow Position 200 200 (mm) Low Pressure (bar) 14 14 High Blow Position 270 270 (mm) High Blow Pressure 40 40 (bar) Preblow Flow (bar) 2 2 Body Mold Temp (° F.) 45 45 Base Mold Temp. (° F.) 45 45 Preform Temp. (° C.) 79 77 Top Weight (g) 8.1 8.1 Panel Weight (g) 22 21.8 Base Weight (g) 10.1 10.4
Twelve bottles were produced at these conditions. The second set of conditions used were the best conditions found that produced bottles with the closest sidewall thicknesses and haze appearance. Six bottles were produced at these conditions.
Analytical Testing--Bottles were placed into an oven set to 125° C. for 24 hours and their dimensional changes were determined. The results from both studies are contained in the following tables.
TABLE-US-00007 Thermal Stability Results (non-Heatset Bottles) Storage Diameter Height Volume Temperature Change Change Change Sample Description (° C.) (%) (%) (%) 25106A1 7032D + Toner 125° C. 0.4 0.5 2.0 25106A2 7032D + toner 125° C. 1.0 1.1 3.8
TABLE-US-00008 Thermal Stability Results (Heatset Bottles) Storage Diameter Height Volume Temperature Change Change Change Sample Description (° C.) (%) (%) (%) 24748A 7000D 150° C. * * * 125° C. * * * 24748B 7032D + 150° C. * * * toner 125° C. 1.0 5.0 4.2
The bases of four of the twelve A1 bottles rolled out during testing causing the bottles to not sit properly on a flat surface. Three of the six A2 bottles tested also rolled out. The amount of shrink was less for these bottles than the bottles that were blown using a heat set process. However, there were no rollout failures in the heatset bottles compared to the 33-50% failure observed in the non-heatset bottles.
Overview--Bottles were made for two PLA materials, 7000D and 7032D PLA supplied by Natureworks, along with a toner/reheat colorant package. Although the 7032D bottles performed better, the thermal stability testing did show a 4.2% shrinkage when those bottles were stored at 125° F.
Injection Molding--Following is a table identifying the variables injection molded during this trial.:
TABLE-US-00009 Material Variables Sample Description 24748A 7000D + toner 24748B 7032D + toner
The PLA resin was dried at 176° F. for 4 hours to remove moisture prior to injection molding. The resin samples were injection molded on an Arburg 420M reciprocating screw injection molding machine using a 40.2±0.5 g preform tooling. An injection molding process was optimized to achieve a clear part at the lowest possible injection molding temperatures and mildest conditions. Following are the preform molding conditions.
TABLE-US-00010 24748 A Natureworks 7000D + 24748 B Colormatrix Natureworks 7032D + Variable Description 80-740-2 Colormatrix 80-740-2 Injection Molding Conditions Injection Date Nov. 26, 2007 Nov. 26, 2007 Machine #6 Arburg 420 M #6 Arburg 420 M Preform # PRE-5568 1 PRE-5568 1 Preform Weight (g) 40.2 40.3 Relative Humidity (% RH) 0% 41% Dew Point (° F.) 0 44 Mold Temp (° F.) 60 60 Ambient Temp (° F.) 0 68.5 Dryer Temp (° F.) 170 170 Barrel Set-point Temperatures Feed (° C.) 211 211 Zone 2 (° C.) 209 210 Zone 3 (° C.) 209 210 Zone 4 (° C.) 211 210 Nozzle (° C.) 206 205 Injection 1st Injection Pressure (bar) 800 800 2nd Injection Pressure (bar) N/A N/A Injection Time (sec) 3.7 3.7 1st Injection Speed (ccm/sec) 12.0 12.0 2nd Injection Speed (ccm/sec) 10.0 10.0 Holding Pressure Switch-Over Point (ccm) 8.0 8.0 1st Hold Pressure (bar) 250.0 250.0 2nd Hold Pressure (bar) 200.0 200.0 3rd Hold Pressure (bar) 100.0 100.0 4th Hold Pressure (bar) N/A N/A 1st Hold Pr. Time (sec) 2.0 2.0 2nd Hold Pr. Time (sec) 3.0 3.0 3rd Hold Pr. Time (sec) 2.0 2.0 4th Hold Pr. Time (sec) 0.0 0.0 Remain Cool Time (sec) 16.0 16.0 Dosage Circumf. Speed (m/min) 10.0 10.0 Back Pressure (bar) 25.0 25.0 Dosage Volume (ccm) 45.0 45.0 Meas. Dosage Time (sec) 6.8 6.1 Cushion (ccm) 7.4 7.6 Adjustment Data Cycle Time (sec) 32.7 32.8
Blow Molding--The PLA preforms were blow molded using a Sidel SBO1 blow molding machine. Initially preforms were blown into a 16 oz Boston round blow mold, CT-5568-1. The initial mold temperature setpoint was 270° F. The mold body temperature was reduced incrementally to 160° F. and the mold base temperature was reduced to 47° F. At these temperatures, the bottles retained their shape after exiting the blow molding machine. The material distribution was difficult to control for the 16 oz container and an excess amount of the material in the neck area of the bottle caused the bottle to not blow fully into the mold. This excess material also did not cool quickly enough in the mold and, therefore, deformed during cooling outside of the mold. The machine speed, oven heating profile and mold temperature were adjusted in an attempt to distribute this material into the rest of the container, but none of the processing changes were successful. As a result, an insert was added to the blow mold to make the bottle longer and provide more area for the material to distribute. Immediately after this insert was added, the excess of material in the neck area was removed and the shoulder was fully blown. Once the 18 oz, CT-5660-0, mold was installed, the processing conditions were optimized to produce bottles with acceptable material distribution. Bottle section weights and sidewall thicknesses were used to determine material distribution. The NatureWorks 7000D bottles were produced using a machine rate of 900 bottles per hour. For the 7032D bottles, two bottles were produced at machine speeds of 900, 700 and 500 bottles per hour. These bottles were filled with hot water at 150° F. and 160° F. The appearance of the bottles produced at 500 bph was better than the two higher machine speeds. This was a result of the slower machine speed and, therefore, more in-mold time allowing stresses to relax. The following table is a summary of blow molding conditions used to produce bottles for testing.
TABLE-US-00011 Blow Molding Conditions Resin Natureworks 7000D + Natureworks 7032D + Colormatrix 80- Colormatrix 80- 740-2 740-2 Speed (bph) 900 500 Overall 45 37 Oven Lamp Settings Zone 8 50 50 Zone 7 45 50 Zone 6 55 45 Zone 5 50 45 Zone 4 40 40 Zone 3 25 25 Zone 2 15 20 Zone 1 100 100 Low Blow Position 270 200 (mm) Low Pressure (bar) 14 14 High Blow Position 255 270 (mm) High Blow Pressure 40 40 (bar) Preblow Flow (bar) 2 2 Body Mold Temp (° F.) 160 160 Base Mold Temp. (° F.) 47 47 Preform Temp. (° C.) 81 77 Top Weight (g) 8 8.2 Panel Weight (g) 21.9 21 Base Weight (g) 10.3 10.7
Drop Impact Testing--To determine the drop impact strength of the containers, bottles were filled with 18 oz. of water, refrigerated for 24 hrs to 40° F. and dropped vertically onto a flat marble platform. A Bruceton staircase method was used to determine the average failure height starting from an initial height of 60 inches using increments of 6 inches. For this method, 21 bottles were dropped. Failure is defined as any leakage of contents not resulting from closure failure. For the 7032 bottles, no failures were observed during the testing. The results are contained in the following table, including those from the previous drop impact testing with the Nalgene® bottles.
TABLE-US-00012 Drop Impact Result Failure Height Work Request Description (in) 23663A 16 oz Nalgene ® 101.0 ± 12.2 24748A 7000D + toner 96.0 ± 10.2 24748B 7032D + toner 114 ± 0
Thermal Stability Testing--Six filled bottles were placed into an oven at 150 or 125° C. for 24 hours and their dimensional changes were determined. At the 150° C. temperature setting, all bottles were distorted and meaningful measurements could not be taken, thus the thermal stability study was repeated at the lower 125° C. temperature to determine the stability there. Bottle diameters and volumes were evaluated both before and after subjecting the bottles to the elevated temperatures. The results are contained in the following table.
TABLE-US-00013 Thermal Stability Results Volume Storage Temperature (° C.) Height Change Description Diameter Change (%) Change (%) (%) 7000D + toner 150° C. * * * 125° C. * * * 7032D + toner 150° C. * * * 125° C. 1.0% 5.0% 4.2
Container Color Testing--Six bottles from the optimized conditions for each material were evaluated for preform color in L*a*b* (CIELAB) color space according to ASTM D1003-61 using a Minolta Color meter. Preforms were cut in half and then placed onto a fixture to allow the sidewall to be flush against the light source. In interpreting this information shown below, the following general guidelines are available:
L: 100=white; 0=blacka*: positive=red; negative=green; 0=grayb*: positive=yellow; negative=blue; 0=gray
Haze--measure of light scattering through the sample; a higher number implies less light going through the sample. The results are contained in the following table.
TABLE-US-00014 Container Color Results Description L* a* b* Haze 7000D + toner 94.97 0.06 1.45 3.67 7032D + toner 95.04 0.08 1.37 3.75
Sidewall Rigidity--Bottles were tested to determine the amount of force required to deflect the sidewall label panel 1/2 inch with a 5/16 inch probe at a crosshead speed of 20 in/min. Test bottles were marked at four locations around the bottle, 90 degrees apart, and the sidewall rigidity was determined at each point. The 0 degree mark is on a parting line. The sidewall rigidity testing has no established specifications.
TABLE-US-00015 Sidewall Rigidity Results 0° 90° 180° 270° Resin Average Average Average Average Description Force (lbf) Force (lbf) Force (lbf) Force (lbf) 7000D + toner 18.4 18.4 18.4 18.0 7032D + toner 19.2 20.2 20.1 18.9
FIGS. 3A-3C show an exemplary embodiment of a PLA bottle 300 produced according to one or more of the manufacturing methods described above. It should be understood that the example of FIG. 3 is just that, an example, an many variations to the size, dimensions, appearance, and look of the example in FIG. 3 are contemplated by the scope of the present disclosure and invention.
While aspects of the present invention have been described with reference to the specific embodiments thereof, it should be understood by those skilled in the art that various changes may be made and equivalents may be substituted without departing from the true spirit and scope of the invention as defined by the appended claims. In addition, many modifications may be made to adapt a particular situation, material, composition of matter, method, process step or steps, to the objective, spirit and scope of the present invention. All such modifications are intended to be within the scope of the claims appended hereto. In particular, while the methods disclosed herein have been described with reference to particular steps performed in a particular order, it will be understood that these steps may be combined, sub-divided, or re-ordered to form an equivalent method without departing from the teachings of the present invention. Accordingly, unless specifically indicated herein, the order and grouping of the steps is not a limitation of the present invention. Specifically, the following options, additional embodiment, and alternatives are contemplated.
The PLA resin may be selected from the class of polyhydroxy alkanoates.
The polylactic acid polymer may be (a) a copolymer having repeating L and D lactic acid units in which either the L or D lactic acid units are the predominant units or (b) a blend of such copolymers wherein the predominant repeating units in the copolymer or blend constitute 90-99.5% of the lactic acid enantiomer repeating units in the PLA resin or blend.
The containers are clear containers capable of passing the industry standards for durable containers.
The containers do not have extractable levels that are suspected or known to have any affect on human health.
The renewable resource based thermoplastic resin has sufficient molecular wt. melt strength and viscosity to successfully produce a durable thick walled container.
The container has sufficient stress induced and quiescent crystallinity to produce a heat stable and impact resistant container capable of meeting the industry performance standards for Polycarbonate bottles.
The PLA resin has a number average molecular wt of 80000-150000 as measured by gel permeation chromatography using a polystyrene standard.
92-99% of the lactic acid enantiomer repeating units in the PLA are of the predominant lactic acid enantiomer.
The formed container has sufficient stress induced and quiescent crystallinity to produce a heat stable and impact resistant container capable of meeting the industry performance standards for Polycarbonate bottles
Patent applications by Greg Roda, Broomfield, CO US
Patent applications in class Applying heat or pressure
Patent applications in all subclasses Applying heat or pressure