US20050221036A1

US20050221036A1 - Polyester composition with enhanced gas barrier, articles made therewith, and methods

Info

Publication number: US20050221036A1
Application number: US11/095,053
Authority: US
Inventors: Yu Shi
Original assignee: Coca Cola Co
Current assignee: Coca Cola Co
Priority date: 2004-04-01
Filing date: 2005-03-31
Publication date: 2005-10-06

Abstract

A polyester composition with enhanced gas barrier properties comprises a polyester and an organic gas barrier enhancing additive having the chemical formula OH-AR—OH, wherein AR is substituted or unsubstituted naphthalene. Articles with enhanced gas barrier and methods for making gas barrier enhanced polyesters and articles are disclosed.

Description

CROSS-REFERENCE

This application claims priority under 35 U.S.C. § 119(e) to U.S. Provisional Application 60/558,494 filed on Apr. 1, 2004, the disclosure of which is expressly incorporated herein by reference in its entirety.

FIELD OF THE INVENTION

This invention relates to polyester and polyester articles. In particular, this invention relates to polyesters for use in applications such as packaged beverages wherein enhanced gas barrier or oxygen scavenging is desirable.

BACKGROUND OF THE INVENTION

Polyethylene terephthalate and its copolyesters (hereinafter referred to collectively as “PET”) are widely used to make containers for carbonated soft drinks, juice, water, and the like due to their excellent combination of clarity, mechanical, and gas barrier properties. In spite of these desirable characteristics, insufficient gas barrier of PET to oxygen and carbon dioxide limits application of PET for smaller sized packages, as well as for packaging oxygen sensitive products, such as food, beer, juice, and tea products. A widely expressed need exists in the packaging industry to further improve the gas barrier properties of PET.
The relatively high permeability of PET to carbon dioxide limits the use of smaller PET containers for packaging carbonated soft drinks. The permeation rate of carbon dioxide through PET containers is in the range of 3 to 14 cc's per day or 1.5 to 2% per week loss rate at room temperature depending on the size of the container. A smaller container has a larger surface to volume ratio resulting in a higher relative loss rate. For this reason, PET containers are currently used only as larger containers for packaging carbonated soft drinks, while metal cans and glass containers are the choice for smaller carbonated soft drink containers.
Numerous technologies have been developed or are being developed to enhance the barrier of PET to small gas molecules. For example, external or internal coatings for enhancing the gas barrier of PET containers have been developed. The coating layer is normally a very high barrier layer, either inorganic or organic, and slows down the diffusion of gases. Implementation of this technology, however, requires coating equipment not normally utilized in the manufacture of packaged beverages and therefore requires substantial capital investment, increased energy usage, and increased floor space. In many beverage packaging plants that are already crowded, the additional space is not an option.
Multi-layered containers have also been developed with a high barrier layer sandwiched between two or more PET layers. Implementation of this technology also requires substantial capital investment and delamination of the container layers impacts appearance, barrier, and mechanical performance of the containers.
A barrier additive for the PET or a polymer with inherent barrier properties would be preferred solutions. Neither such solution requires additional capital investment, and therefore, does not have the limitations inherent with other technologies. A barrier additive can also be added during the injection molding process which gives more flexibility for downstream operations.
L. M. Robeson and J. A. Faucher disclose in J. Polymer Science, Part B 7, 35-40 (1969) that certain additives could be incorporated into polymers to increase their modulus and gas barrier properties through an antiplasticization mechanism. This article discloses utilizing additives with polycarbonate, polyvinyl chloride, polyphenylene oxide, and polythyelene oxide.
In WO 01/12521, Plotzker et al. proposed the use of additives selected from 4-hydroxybenzoates and related molecules to increase the gas barrier properties of PET. This published patent application discloses barrier additives of the following structure:
HO—Ar—COOR, HO—Ar—COOR1COO-AR—OH, HO-AR—CONHR, HO-AR—CO—NHR3-COO-AR—OH, HO-AR—CONHR2NHCO-AR—OH
In the foregoing structure, AR is selected from the group consisting of substituted or unsubstituted phenylene or naphthalene. And R1, R2, and R3 are selected from the group consisting from C1 to C6 alkyl groups, a phenyl group, and a naphthyl group.
The foregoing additives described in the art provide only moderate improvement in PET barrier, less than 2.1 times (×) for oxygen barrier for the best examples with a 5 weight percent loading level. At this loading level, however, PET experiences substantial degradation and a significant drop in intrinsic viscosity (IV). Although lowering the level of additive reduces the degradation of PET, it also reduces the barrier improvement factor, so much so that no real benefit exists in using these additives in packaging carbonated soft drinks or oxygen sensitive food. Furthermore, PET with a significantly lower IV cannot be used in blow molding containers, such as beverage containers. Furthermore, lower IV PET makes containers with poor mechanical performance, such as creep, drop impact, and the like. Still further, PET containers made from lower IV PET have poor stress cracking resistance, which is undesirable in container applications.
PET has been modified or blended with other components to enhance the gas barrier of the PET. Examples include polyethylene naphthalate (PEN)/PET copolymers or blends, isophthalate (IPA) modified PET, PET blended with polyethylene isophthalate (PEI) or a polyamide, such as nylon, and PET modified with resorcinol based diols. For a PET copolymer to achieve moderate barrier enhancement of 2× or higher, the modification is normally more than 10 to 20 weight or mole % of the total co-monomers. When PET is modified to such a high level, the stretching characteristics of the PET are changed dramatically such that the normal PET container preform design could not be used in the manufacture of containers. Using these PET copolymers to mold conventional PET container preforms results in preforms that can not be fully stretched and the ultimate containers are very difficult, if not impossible, to make. Even if such a container can be made, it does not show improved barrier performance and shows deteriorated physical performance such that it can not be used to package carbonated soft drinks. U.S. Pat. Nos. 5,888,598 and 6,150,450 disclose redesigned PET container preforms with thicker side walls to compensate for the increased stretch ratio. This thicker preform, however, requires new molds which require additional capital investment and is also made at a lower rate of productivity because it takes longer to cool and heat the thicker wall preform. Furthermore, PET blends with polyamide such as nylon developed yellowness and haze and are not clear like conventional PET.
Products sensitive to oxygen, such as foods, beverages and medicines, deteriorate and spoil in the presence of oxygen. To prevent oxygen ingress to the products, different oxygen scavenger technologies have been developed. These oxygen scavengers are called active barrier technologies. They are different from the passive barrier technologies that work to improve barrier to small gas molecules only. U.S. Pat. No. 5,021,515 discloses a multi-layered, nylon based oxygen scavenger. U.S. Pat. No. 5,744,056 discloses an oxygen scavenger composition that can be incorporated into bottle sidewall in a monolayer fashion. Similarly, U.S. Pat. No. 5,700,554 discloses an oxygen scavenger composition. The monolayer oxygen scavengers provide additional benefits over the multi-layered oxygen scavenger in that the monolayer oxygen scavenger can react with the headspace oxygen in the container, in addition to blocking the oxygen ingress to the container. Therefore, the monolayer oxygen scavenger can prevent the product oxidation from the headspace oxygen. The oxygen scavenger compositions disclosed in these and other similar patents, however, all contain transition metals as catalysts. The transition metals can cause degradation in PET and cause discoloration in PET. In addition, in certain countries, certain transition metals also raise environmental and regulatory concerns.
Thus, there is a need in the art to enhance the barrier performance of PET for use in applications that will require enhanced barrier, such as in the packaging of carbonated beverages and oxygen sensitive beverages and foods, in a manner that does not cause substantial degradation of the PET, does not substantially impact the stretch ratio of the PET, does not include transition metals, and allows the use of existing PET perform toolings.

SUMMARY OF THE INVENTION

This invention addresses the above described need for enhanced gas barrier PET by providing a polyester composition comprising a polyester and an organic gas barrier enhancing additive having the chemical formula OH-AR—OH, wherein AR is substituted or unsubstituted naphthalene.
In accordance to a particular embodiment, the polyester in the polyester composition comprises a poly(ethylene terethphalate) based copolymer (PET copolymer). In a desired embodiment, the polyester comprises a PET copolymer having less than 20% diacid component modification and/or less than 10% diol component modification, based on 100 mole % diacid component and 100 mole % diol component. With the organic gas barrier enhancing additive, this embodiment provides acceptable gas barrier despite having a low level of diacid or diol modification, if any modification. Without wishing to be bound by theory, it is believed that some embodiments of this invention possess gas barrier capability, while another possesses more oxygen scavenging capability or both gas barrier and oxygen scavenging capability.
According to another embodiment, this invention encompasses a method for enhancing gas barrier of a polyester composition comprising blending a polyester and an organic gas barrier enhancing additive having the chemical formula OH-AR—OH, wherein AR is substituted or unsubstituted naphthalene. According to a preferred embodiment, the polyester is a PET copolymer.
According to still another embodiment, this invention encompasses an article comprising a polyester and an organic gas barrier enhancing additive having the chemical formula OH-AR—OH, wherein AR is substituted or unsubstituted naphthalene. According to a particular embodiment, the article is a container and in other preferred embodiments is a stretch blow molded container. In a preferred embodiment, the polyester is a PET copolymer.
According to yet another embodiment, this invention encompasses a method for making an article with enhancing gas barrier comprising the steps of blending a polyester and an organic gas barrier enhancing additive having the chemical formula OH-AR—OH, wherein AR is substituted or unsubstituted naphthalene. In a particular embodiment, the polyester is a PET copolymer. Furthermore, in another embodiment, the article is a stretch blow molded container.
Particular embodiments of this invention provide polyesters, such as PET copolymers, with enhanced gas barrier, and in particular, enhanced barrier to carbon dioxide and oxygen. This makes certain embodiments of this invention particularly suited for packaging carbonated soft drinks and oxygen sensitive beverages and foods. Particular embodiments achieve this enhanced gas barrier while maintaining acceptable physical properties.
Other objects, features, and advantages of this invention will become apparent from the following detailed description, drawings, and claims.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic illustration of a system for making a PET container with enhanced gas barrier in accordance with an embodiment of this invention.
FIG. 2 is a sectional elevation view of a molded container preform made in accordance with an embodiment of this invention.
FIG. 3 is a sectional elevation view of a blow molded container made from the preform of FIG. 2 in accordance with an embodiment of this invention.
FIG. 4 is a perspective view of a packaged beverage made in accordance with an embodiment of this invention.

DETAILED DESCRIPTION OF EMBODIMENTS

This invention encompasses a polyester composition with enhanced gas barrier or oxygen scavenging capability or both, a method for enhancing gas barrier or oxygen scavenging capability of a polyester composition, articles comprising such a polyester composition, and a method for making such articles. As explained in more detail below, embodiments of this invention provide a polyester composition and articles made therewith which exhibit enhanced barrier to gases or oxygen scavenging capability while maintaining physical properties.
This invention is applicable to any polyester and is suitable for uses in which a high gas barrier is desirable. Suitable polyesters include those that are suitable for packaging carbonated or non-carbonated beverages and oxygen sensitive beverages or food products. Suitable polyesters for use in embodiments of this invention include PET copolymers, polyethylene naphthalate (PEN), polyethylene isophthalate, and the like. PET copolymers are particularly useful because they are used for many barrier applications such as films and containers. Suitable containers include but are not limited to bottles, drums, carafes, coolers, and the like.
PET copolymers suitable for use in embodiments of this invention comprise a diol component having repeat units from ethylene glycol and a diacid component having repeat units from terephthalic acid. Desirably, in some embodiments, the PET copolymer has less than 20% diacid component modification and/or less than 10% diol component modification, based on 100 mole % diacid component and 100 mole % diol component. Such PET copolymers are well known.
In accordance with embodiments of this invention, suitable organic gas barrier enhancing additives are those having the chemical formula OH-AR—OH, wherein AR is substituted or unsubstituted naphthalene. Suitable additives include, but are not limited to, 1,2-dihydroxy naphthalene, 1,3-dihydroxy naphthalene, 1,5-dihydroxy naphthalene, 1,6-dihydroxy naphthalene, and 2,6-dihydroxy naphthalene. 1,5-dihydroxy naphthalene degrades at polyester melt processing temperatures, and therefore is not a preferred additive, but is useful at lower melt processing temperatures. 2,7-dihydroxy naphthalene is not listed because it has an even lower degradation temperature and is not suitable for use as an additive for PET.
The organic gas barrier enhancing additive compound is added to the polyester in an amount sufficient to enhance the gas barrier properties of the polyester. In accordance with an embodiment of this invention, the polyester is present in the polyester composition in amount from 99.9% to 90% by weight of the polyester composition and the organic gas barrier enhancing additive is present in the polyester composition in an amount of 0.1% to about 10% by weight of the polyester composition. In accordance to another embodiment of this invention, the PET copolymer is present in the polyester composition in an amount from 99.9% to about 95% by weight of the polyester composition and the additive is present in the polyester composition in an amount from about 0.1% to about 5% by weight of the polyester composition. In accordance with still another embodiment of this invention, the PET copolymer is present in the polyester composition in an amount from about 99.9% to about 97% by weight of the polyester composition and the additive is present in the polyester composition in an amount from about 0.1% to about 3% by weight of the polyester composition.
Polyesters, including PET copolymers, have free volume between polymer chains. As is known to those skilled in the art, the amount of free volume in polyesters such as PET copolymers determines their barrier to gas molecules. The lower the free volume, the lower the gas diffusion, and the higher the barrier to gas molecules. In some embodiments, it is believed that the additive is at least partially disposed in the free volume of the polyester between the polyester chains and solidifies in the free volume when the blend is cooled down to room temperature after melt processing. Due to the presence of the two hydroxyl groups, it is possible that the additive reacts with the polyester chain and causes the intrinsic viscosity (IV) to drop although the reactivity of the hydroxy group in the current additive is very low. Therefore, when melt blending the additive with polyester, it is possible that the additive partially reacts with the polyester and forms a mixture of polyester/dihydroxy naphthalene copolymer, polyester, and the additive. For example, when the additive is 1,3-dihydroxy naphthalene, it is believed that the additive at least partially reacts with the polyester and becomes part of the polyester backbone chain. According to a particular embodiment, the polyester comprises a poly(ethylene terephthalate) based copolymer (PET copolymer) and, based on 100 mole % diacid component and 100 mole % diol component, the PET copolymer has less than 20% diacid component modification and less than 10% diol component modification, and at least a portion of the additive is reacted with the PET copolymer such that the diol component comprises 0.1 to about 5 mole % of the additive.
The additive may be incorporated into the polyester in different ways. For example, at lower loading levels, i.e., 3 weight % or below, the additive can be incorporated directly into polyester during the injection molding process, can be preblended in the polyester resin making process, or can be incorporated into melt polyester prior to the discharge of the polyester in the melt polymerization process. At higher loading levels, 3 weight % or higher, the additives can be preblended with the polyester, melt extruded and solid state polymerized to the desired IV. The solid stated mixture can then be injection molded into container performs as described in more detail below.
In some embodiments, it is desirable to reduce the latent effect of any residual polycondensation catalyst in the polyester. These catalysts include commonly used catalyst such as compounds containing antimony, titanium, tin, and the like, and are deactivated by phosphorus containing compounds. The phosphorus containing compounds include both organic and inorganic compounds. Examples include but are not limited to phosphoric acid, polyphosphoric acid, and tris(2,4-di-t-butylphenyl) phosphite, tris monononylphenyl phosphite. These additives are typically added in amounts less than 2000 ppm.
As described above, the polyester composition of this invention is useful for making articles in which enhanced gas barrier is desirable. In short, such articles are made by forming the above described polyester compositions into the desired article by conventional methods such as melt forming. Suitable melt forming processes include, but are not limited to, injection molding, extrusion, thermal forming and compression molding.
In particular, embodiments of this invention are suitable for making containers for packaging applications in the carbonated and non-carbonated soft drink industry and the food industry. A common manufacturing method for forming these containers includes injection molding container preforms, and then, making the containers from the preforms in single stage, two stage, and double blow molding manufacturing systems. Such methods are well known to those skilled in the art and examples of suitable preform and container structures and are disclosed in U.S. Pat. No. 5,888,598, the disclosure of which is expressly incorporated herein by reference in its entirety.
More particularly, a container preform is formed by injection molding the polyester into a blowable geometric form. The preform or blowable form is then contained within a mold cavity having the volumetric configuration of the desired container and the preform is expanded by blowing it with compressed air within the confines of the mold cavity.
Commercially available equipment, as is used in the manufacture of thin walled single use PET beverage containers, may be used to make the containers in accordance with embodiments of the present invention. In addition, commercial equipment like that used in manufacturing conventional thick wall refillable PET containers may also be used.
Suitable containers in accordance with embodiments of this invention may be blow-molded from a cylindrical injection-molded preform having an open top end and neck finish. The preform may have a tapered shoulder-forming portion, substantially uniform thickness along the sides of the cylinder, and a base-forming portion preferably in a champagne design, but including a hemispherical base with a base cup or a footed design such as a petaloid design. In preferred embodiments, the preform is amorphous and substantially transparent and is injection molded.
In accordance with preferred embodiments of this invention, container preforms are subsequently placed in a blow molding apparatus having an upper mold section which engages the neck finish, a middle mold section having an interior cavity forming the shape of the container side wall, and a lower mold section having an upper surface forming the outwardly concave dome portion of the container base. In accordance with a standard reheat stretch blow mold process, the injection-molded preform is first reheated to a temperature suitable for stretching and orientation of about 70 to 130° C., placed in the blow mold, and an axial stretch rod is then inserted into the open upper end and moved downwardly to axially stretch the preform. Subsequently or simultaneously, an expansion gas is introduced into the interior of the preform to radially expand the shoulder, sidewall and base forming portions outwardly into contact with the interior surfaces of mold sections. The resulting blown container has the same neck finish with outer threads and lowermost neck flange as the preform. The remainder of the bottle undergoes expansion, although to varying degrees. A removable cap is attached to the open upper end of the container. The cap includes a base portion having internal threads which engage the outer threads on the neck finish.
FIG. 1 illustrates a system 10 in accordance with an embodiment of this invention for making a rigid container preform 12 (illustrated in FIG. 2) and a rigid container 14 (illustrated in FIG. 3) from the preform. As is shown in FIG. 1, solid PET copolymer pellets 20 and an organic gas barrier enhancing additive such as dimethyl terephthalate 22 are added to a feeder or hopper 24 that delivers the components to a hot melt extruder 26 in which the components are melted and blended. The hot melt extruder 26 then extrudes the molten mixture of PET copolymer and organic gas barrier enhancing additive into an injection molding device 28 to form the preform 12. The preform is cooled and removed from the injection molding device 28 and delivered to a blow molding device 30 which blow molds the preform 12 into a finished rigid container 14.
As explained above, the melt residence time of the preform production is preferably less than three minutes and more preferably from about 100 to about 120 seconds. The melt temperatures desirably from 270 to about 300° C. and more desirably from about 270 to about 290° C. The melt residence time begins when the PET copolymer and organic barrier enhancing additive enter the melt extruder 26 and start melting, and ends after injection of the molten blend into the injection mold to form the preform 12.
Turning to FIG. 2, a polyester container preform 12 is illustrated. This preform 12 is made by injection molding PET based resin and comprises a threaded neck finish 112 which terminates at its lower end in a capping flange 114. Below the capping flange 114, there is a generally cylindrical section 116 which terminates in a section 118 of gradually increasing external diameter so as to provide for an increasing wall thickness. Below the section 118 there is an elongated body section 120.
The preform 12 illustrated in FIG. 2 can be blow molded to form a container 14 illustrated in FIGS. 3 and 4. The container 14 comprises a shell 124 comprising a threaded neck finish 126 defining a mouth 128, a capping flange 130 below the threaded neck finish, a tapered section 132 extending from the capping flange, a body section 134 extending below the tapered section, and a base 136 at the bottom of the container. The container 14, for the most part, is highly biaxially oriented, but the neck finish 126 is non-oriented. The container 14 is suitably used to make a packaged beverage 138, as illustrated in FIG. 4. The packaged beverage 138 includes a beverage such as a carbonated soda beverage disposed in the container 14 and a closure 140 sealing the mouth 128 of the container.
The preform 12, container 14, and packaged beverage 138 are but examples of applications using the preforms of the present invention. It should be understood that the process and apparatus of the present invention can be used to make preforms and containers having a variety of configurations.
The present invention is described above and further illustrated below by way examples which are not to be construed in any way as imposing limitations upon the scope of the invention. On the contrary, it is to be clearly understood that resort may be had to various other embodiments, modifications, and equivalents thereof which, after reading the description herein, may suggestion themselves to those skilled in the art that without departing from the scope of the invention and the appended claims.

EXAMPLE 1

A commercially available polyester container grade resin was used as a control. The polyester composition (PET) had a diacid component of 97.2 mole % terephthalic acid and 2.8 mole % isophthalic acid and a glycol component of 97.2 to 97.3 mole % ethylene glycol and 2.7 to 2.8 mole % diethylene glycol. The PET was dried in a vacuum oven at 140° C. overnight to a moisture level below 50 ppm. The additives listed in Table 1 were dried in a vacuum oven at 70° C. overnight to remove absorbed moisture. The PET and 5 weight % of different additives were mixed prior to injection molding. A lab scale Arburg unit cavity injection molding machine was used for injection molding. A 24.5-g preform was used to make a 500 ml container. The preforms were blow molded with a Sidel SBO 2/3 blow molding machine to make acceptable 500 ml contour containers. The oxygen transmission rate of the containers was then measured using a Macon 2/60 model instrument at 22.2° C. and 50% relative humidity (RH) with the 99% N₂/1% H₂purging rate of 10 ml/min on one side and air on the other side. The results are shown in Table 1. The barrier improvement factor (BIF) was defined as the ratio of the oxygen transmission rate of the control and the additive package. BIF is a measurement of the barrier enhancement as comparison to control.
Table 1 Oxygen transmission rate of the control and additive containers at 5 weight % additive loading

TABLE 1

O₂transmission rate Barrier Improvement

Additive (cc/pkg/day) Factor (BIF)

PET Control 0.046 1.00

1,5 dihydroxy naphthalene 0.0097 4.74

1,6 dihydroxy naphthalene 0.005 9.20

2,6 dihydroxy naphthalene 0.0064 7.19

EXAMPLE 2

The resins and additives listed in Table 2 were dried, mixed and injection molded as in Example 1. Instead of 5 weight % of additive loading, a 3 weight % of additive loading was used. A 24.5-g preform was used to make a 500 ml container. The preforms were blow molded with a Sidel SBO 2/3 blow molding machine to make acceptable 500 ml contour containers. The oxygen transmission rate of the containers was then measured using a Macon 2/60 model instrument at 22.2° C. and 50% RH with the 99% N₂/1% H₂purging rate of 10 ml/min on one side and air on the other side. The results are shown in Table 2.

TABLE 2

Oxygen transmission rate of the control and additive

containers at 3 weight % additive loading

O₂transmission rate Barrier Improvement

Additive (cc/pkg/day) Factor (BIF)

PET control 0.046 1.0

1,6 dihydroxy naphthalene 0.008 5.75

2,6 dihydroxy naphthalene 0.008 5.75

EXAMPLE 3

A commercially available carbonated soft drink grade PET resin and 3 weight % 1,3-dihydroxy naphthalene were dried, mixed and injection molded as in Example 1. A 24.5 g preform was used to make a 500 ml container. The preforms were blow molded with a Sidel SBO 2/3 blow molding machine to make acceptable 500 ml contour containers. The bottle sidewalls were then cut into a 2 in by 2 in square and mounted into a Mocon Permeatran to measure the CO₂transmission rate. A PET control film was also used for the CO₂transmission rate. The results are shown in table 3.

TABLE 3

CO₂transmission rate of the control and additive films

CO₂transmission rate Barrier Improvement

Additive (cc/mil/100 in²/day) Factor (BIF)

PET control 29.1 1.0

3 weight % 1,3 13.7 2.12

dihydroxy naphthalene

EXAMPLE 4

A commercially available carbonated soft drink grade PET resin and 5 weight % of 1,3 dihydroxy naphthalene additive were dried, mixed and injection molded as in Example 1. A 24.5-g preform was used to make a 500 ml container. The preforms were blow molded with a Sidel SBO 2/3 blow molding machine to make acceptable 500 ml contour containers. The oxygen transmission rate of the containers were then measured using a Macon 2/60 model instrument at 22.2° C. and 50% RH with the 99% N₂/1% H₂purging rate of 10 ml/min on one side and air on the other side. The results are shown in Table 4.

TABLE 4

Oxygen transmission rate of the control and additive containers

O₂transmission Barrier Improvement

Additive rate (cc/pkg/day) Factor (BIF)

PET control 0.046 1.00

5 weight % 1,3 dihydroxy 0.0000 NA

naphthalene
Surprisingly, the 5 weight % 1,3 dihydroxy naphthalene gave unexpected low oxygen transmission rate. The O₂transmission rate was too low to be detected from the measurement equipment. This clearly showed an oxygen scavenger effect. This oxygen scavenger composition has the added benefit over the prior art oxygen scavenger composition in that it does not contain any transition metals.

EXAMPLE 5 (COMPARISON EXAMPLES)

The resins and additives were dried, mixed and injection molded as in Example 1. Two comparison additives were used. One was selected from the best performing additive list from WO 01/12521, methyl-4-hydroxy-benzonate. Another was selected from a high barrier comonomer from U.S. Pat. No. 6,320,014, 1,3-dihydroxy benzene. The additives were added at 3 weight % first, then at 5 weight %. When added at 5 weight %, excessive degradation occurred for the 1,3-dihydroxy benzene. The excessive degradation caused substantial IV drop so much so that acceptable containers could not be made. A 24.5-g preform was used to make a 500 ml container. The preforms were blow molded with a Sidel SBO 2/3 blow molding machine to make acceptable 500 ml contour containers. The oxygen transmission rate of the containers were then measured using a Macon 2/60 model instrument at 22.2° C. and 50% RH with the 99% N₂/1% H₂purging rate of 10 ml/min on one side and air on the other side. The results are shown in Table 5.

TABLE 5

Comparison oxygen transmission

rate for the control and additive containers

Barrier

O₂transmission Improvement

Additive Loading rate (cc/pkg/day) Factor (BIF)

PET control 0.046 1.00

1,3 dihydroxy 3 wt % 0.034 1.35

benzene

Methyl-4-hydroxy 5 wt % 0.023 2.00

benzoate

Methyl-4-hydroxy 3 wt % 0.03 1.53

benzoate
As can be seen from the data in table 5, embodiments of this invention have much higher gas barrier than containers made with conventional barrier additives.
It should be understood that the foregoing relates to particular embodiments of the present invention, and that numerous changes may be made therein without departing from the scope of the invention as defined by the following claims.

Claims

1. A polyester composition comprising:

a polyester; and

an organic gas barrier enhancing additive having the chemical formula OH-AR—OH, wherein AR is substituted or unsubstituted naphthalene.

2. A polyester composition as in claim 1 wherein the polyester is present in the polyester composition in an amount from about 99.9% to about 90% by weight of the polyester composition and the additive is present in the polyester composition in an amount from about 0.1% to about 10% by weight of the polyester composition.

3. A polyester composition as in claim 1 wherein the additive is selected from the group comprising 1,2-dihydroxy naphthalene, 1,3-dihydroxy naphthalene, 1,5-dihydroxy naphthalene, 1,6-dihydroxy naphthalene, and 2,6-dihydroxy naphthalene.

4. A polyester composition as in claim 1 wherein the additive is 1,3-dihydroxy naphthalene.

5. A polyester composition as in claim 1 wherein the polyester comprises a poly(ethylene terephthalate) based copolymer (PET copolymer) having less than 20% diacid component modification and/or less than 10% diol component modification, based on 100 mole % diacid component and 100 mole % diol component.

6. A polyester composition as in claim 5 wherein the PET copolymer is present in the polyester composition in an amount from about 99.9% to about 90% by weight of the polyester composition and the additive is present in the polyester composition in an amount from about 0.1% to about 10% by weight of the polyester composition.

7. A polyester composition as in claim 5 wherein the PET copolymer is present in the polyester composition in an amount from about 99.9% to about 95% by weight of the polyester composition and the additive is present in the polyester composition in an amount from about 0.1% to about 5% by weight of the polyester composition.

8. A polyester composition as in claim 5 wherein the PET copolymer is present in the polyester composition in an amount from about 99.9% to about 97% by weight of the polyester composition and the additive is present in the polyester composition in an amount from about 0.1% to about 3% by weight of the polyester composition.

9. A polyester composition as in claim 5 wherein the additive is selected from the group comprising 1,2-dihydroxy naphthalene, 1,3-dihydroxy naphthalene, 1,5-dihydroxy naphthalene, 1,6-dihydroxy naphthalene, and 2,6-dihydroxy naphthalene.

10. A polyester composition as in claim 1 wherein the polyester has a free volume and at least a portion of the additive is unreacted with the polyester and disposed in the free volume of the polyester.

11. A polyester composition as in claim 1 wherein the polyester comprises a poly(ethylene terephthalate) based copolymer (PET copolymer) and, based on 100 mole % diacid component and 100 mole % diol component, the PET copolymer has less than 20% diacid component modification and less than 10% diol component modification, and at least a portion of the additive is reacted with the PET copolymer such that the diol component comprises 0.1 to about 5 mole % of the additive.

12. Method for enhancing gas barrier or gas scavenging capability of a polyester composition comprising blending a polyester and an organic gas barrier enhancing additive having the chemical formula OH-AR—OH, wherein AR is substituted or unsubstituted naphthalene.

13. Method as in claim 12 wherein the polyester is present in the polyester composition in an amount from about 99.9% to about 90% by weight of the polyester composition and the additive is present in the polyester composition in an amount from about 0.1% to about 10% by weight of the polyester composition.

14. Method as in claim 12 wherein the additive is selected from the group comprising 1,2-dihydroxy naphthalene, 1,3-dihydroxy naphthalene, 1,5-dihydroxy naphthalene, 1,6-dihydroxy naphthalene, and 2,6-dihydroxy naphthalene.

15. Method as in claim 12 wherein the additive is 1,3-dihydroxy naphthalene.

16. Method as in claim 12 wherein the polyester comprises a poly(ethylene terephthalate) based copolymer (PET copolymer) having less than 20% diacid component modification and/or less than 10% diol component modification, based on 100 mole % diacid component and 100 mole % diol component.

17. Method as in claim 16 wherein the PET copolymer is present in the polyester composition in an amount from about 99.9% to about 90% by weight of the polyester composition and the additive is present in the polyester composition in an amount from about 0.1% to about 10% by weight of the polyester composition.

18. Method as in claim 16 wherein the PET copolymer is present in the polyester composition in an amount from about 99.9% to about 95% by weight of the polyester composition and the additive is present in the polyester composition in an amount from about 0.1% to about 5% by weight of the polyester composition.

19. Method as in claim 16 wherein the PET copolymer is present in the polyester composition in an amount from about 99.9% to about 97% by weight of the polyester composition and the additive is present in the polyester composition in an amount from about 0.1% to about 3% by weight of the polyester composition.

20. Method as in claim 16 wherein the additive is selected from the group comprising 1,2-dihydroxy naphthalene, 1,3-dihydroxy naphthalene, 1,5-dihydroxy naphthalene, 1,6-dihydroxy naphthalene, and 2,6-dihydroxy naphthalene.

21. Method as in claim 12 wherein the polyester has a free volume and at least a portion of the additive is unreacted with the polyester and disposed in the free volume of the polyester.

22. Method as in claim 12 wherein the polyester comprises a poly(ethylene terephthalate) based copolymer (PET copolymer) and, based on 100 mole % diacid component and 100 mole % diol component, the PET copolymer has less than 20% diacid component modification and less than 10% diol component modification, and at least a portion of the additive is reacted with the PET copolymer such that the diol component comprises 0.1 to about 5 mole % of the additive.

23. A container comprising a polyester composition comprising:

a polyester; and

24. A container as in claim 23 wherein the container is a stretch blow molded container comprising a base, an open ended mouth, and a body extending from the base to the open ended mouth.

25. A container as in claim 23 wherein the polyester is present in the polyester composition in an amount from about 99.9% to about 90% by weight of the polyester composition and the additive is present in the polyester composition in an amount from about 0.1% to about 10% by weight of the polyester composition.

26. A container as in claim 23 wherein the additive is selected from the group comprising 1,2-dihydroxy naphthalene, 1,3-dihydroxy naphthalene, 1,5-dihydroxy naphthalene, 1,6-dihydroxy naphthalene, and 2,6-dihydroxy naphthalene.

27. A container as in claim 23 wherein the polyester comprises a poly(ethylene terephthalate) based copolymer (PET copolymer) having less than 20% diacid component modification and/or less than 10% diol component modification, based on 100 mole % diacid component and 100 mole % diol component.

28. A container as in claim 27 wherein the PET copolymer is present in the polyester composition in an amount from about 99.9% to about 90% by weight of the polyester composition and the additive is present in the polyester composition in an amount from about 0.1% to about 10% by weight of the polyester composition.

29. A container as in claim 27 wherein the PET copolymer is present in the polyester composition in an amount from about 99.9% to about 95% by weight of the polyester composition and the additive is present in the polyester composition in an amount from about 0.1% to about 5% by weight of the polyester composition.

30. A container as in claim 27 wherein the PET copolymer is present in the polyester composition in an amount from about 99.9% to about 97% by weight of the polyester composition and the additive is present in the polyester composition in an amount from about 0.1% to about 3% by weight of the polyester composition.

31. A container as in claim 27 wherein the additive is selected from the group comprising 1,2-dihydroxy naphthalene, 1,3-dihydroxy naphthalene, 1,5-dihydroxy naphthalene, 1,6-dihydroxy naphthalene, and 2,6-dihydroxy naphthalene.

32. A container as in claim 23 wherein the polyester has a free volume and at least a portion of the additive is unreacted with the polyester and disposed in the free volume of the polyester.

33. A container as in claim 23 wherein the polyester comprises a poly(ethylene terephthalate) based copolymer (PET copolymer) and, based on 100 mole % diacid component and 100 mole % diol component, the PET copolymer has less than 20% diacid component modification and less than 10% diol component modification, and at least a portion of the additive is reacted with the PET copolymer such that the diol component comprises 0.1 to about 5 mole % of the additive.