Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Reexamination Certificate
2000-08-09
2002-12-03
Michl, Paul R. (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
C524S222000
Reexamination Certificate
active
06489386
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention is a polymer composition and method for improving the gas barrier performance of polymeric containers and films, and particularly containers for food and beverages which are molded from thermoplastic polyester polymers. More particularly, the invention is a polymer composition and method for reducing the permeability of gases through molded polymeric containers, sheets and films by incorporating into the polymer from which the container, sheet or film is formed an effective amount of a barrier-enhancing additive of the type described herein.
The addition of small amounts of molecular additives to a base polymer can result in antiplasticization of the polymer whereby the modulus of the polymer increases below its glass transition temperature and its barrier to gas permeability can improve. For example, Robeson describes the use of phenyl-2-naphthyl amine in polysulfone [Robeson, L. M.; Faucher, J. A.,
J. Polym. Sci.,
Part B 7, 35-40 (1969)] and various polychlorinated aromatic molecules in polycarbonate and in polyvinyl chloride [Robeson, L. M.,
Polym. Eng. Sci.
9, 277-81 (1969)]. Maeda and Paul [Maeda, Y.; Paul, D. R.,
J Polym. Sci.,
Part B:
Polym. Phys.
25, 981-1003 (1987)] disclose the use of tricresyl phosphate in polyphenylene oxide to lower the sorption of carbon dioxide (and therefore its permeability). However, the need exists to improve the gas barrier performance of polymer resins of the type currently used for molded containers for food and beverages, and, in particular, poly(ethylene) terephthalate (PET) thermoplastic polyester polymers used for producing injection stretch blow molded bottles for packaging water, carbonated soft drinks and beer. Additives selected from 4-hydroxybenzoates and related molecules of the type described herein have not been suggested.
SUMMARY OF THE INVENTION
The present invention and the inventive features described herein reside in the discovery of certain barrier-enhancing additives for thermoplastic polymers. The invention is a polymer composition that contains one or more of the additives and a method for reducing gas permeability of shaped polymeric articles produced from such a composition, such articles being generally selected from containers, sheets and films.
The method comprises incorporating into the polymer an effective amount of a barrier-enhancing additive, or a mixture of barrier-enhancing additives, selected from the group consisting of:
(a) monoesters of hydroxybenzoic acid and hydroxynaphthoic acid of the formula (A)
wherein R is C
1
-C
8
alkyl, benzyl, phenyl or naphthyl; Ar is substituted or unsubstituted phenylene or naphthalene; or formula (AA) where M is a cation such as, but not limited to, sodium, ammonium, tetraalkyl ammonium, potassium, calcium, magnesium or zinc;
(b) diesters of hydroxybenzoic acid of the formula (B)
wherein Ar is as defined above, and R
1
is C
1
-C
8
alkyl, (CH
2
CH
2
O)
k
CH
2
CH
2
where k is 1 or more, benzyl, phenyl or naphthyl; or formula (BB) where M is as defined above.
(c) monoamides of hydroxybenzoic acid and hydroxynaphthoic acid of the formula (C)
wherein R and Ar are as defined above; or formula (CC) where M is as defined above.
(d) diamides of hydroxybenzoic acid of the formula (D)
wherein Ar is as defined above, and R
2
is C
1
-C
8
alkyl, (CH
2
CH
2
O)
k
CH
2
CH
2
where k is 1 or more, benzyl, phenyl or naphthyl; or formula (DD) where M is as defined above.
(e) ester-amides of hydroxybenzoic acid of the formula (E)
where Ar is as defined above and R
3
is C
1
-C
8
alkyl, C
1
-C
8
dialkyl, (CH
2
CH
2
O)
k
CH
2
CH
2
where k is 1 or greater, benzyl, phenyl or naphthyl, or formula (EE) where M is as defined above. As used herein, an effective amount, i.e., the preferred range of barrier enhancing additive, is from 0.1% by wt. to 20% by wt. of the base polymer comprising the polymeric article.
Polymeric articles, and particularly extruded film or injection stretch blow molded polyester (e.g., PET) bottles, which contain one or more of the barrier-enhancing additives described herein, exhibit substantially reduced oxygen and carbon dioxide permeability values when measured according to ASTM D3985 and water vapor permeability values when measured according to ASTM F1249 in comparison to corresponding polymeric articles which contained no barrier-enhancing additives.
DETAILED DESCRIPTION OF THE INVENTION
The present invention resides in the discovery that oxygen, water vapor and carbon dioxide (CO
2
) permeability values for shaped polymeric containers and films can be substantially reduced by incorporating into the base polymer from which the articles are formed from about 0.1% by wt. up to about 20% by wt. of a barrier-enhancing additive of the type defined herein.
A uniform physical blend, or mixture, is prepared comprising the base polymer and one or more barrier-enhancing additives in the desired concentrations. As used herein with reference to the invention, the term “composition” is intended to mean a physical blend or mixture. Water-sensitive base polymers, such as, for example, polyesters should preferably be thoroughly dried by heating under air or nitrogen flow or vacuum as known to those experienced in the art. The mixture is then heated and extruded or molded at a sufficiently high temperature to melt the base polymer and provide for sufficient mixing of the additive or mixture of additives within the base polymer matrix. By way of example using PET, such melt temperature ranges from about 255° C. to 300° C. The composition thus produced comprises the barrier-enhancing additive (or mixture of such additives) substantially in its (their) original molecular form; that is, only small amounts of barrier-enhancing additive have been observed to react with the base polymer via trans-esterification or other reaction mechanism typical of the functional groups present. It is preferred to prepare and extrude or mold the polymer composition under conditions of relatively low temperature and processing residence time which thereby minimizes the opportunity for the barrier-enhancing additives to react with the base polymer. Best performance in terms of desirable mechanical properties of polymeric containers and films produced according to the invention is achieved when no more than about 10% of the gas barrier-enhancing additive has reacted with the base polymer. As a consequence of any reaction of a gas barrier-enhancing additive within the scope of the invention with a base polymer, the molecular weight of the starting base polymer may decrease.
The gas barrier-enhancing additives found to be most suitable for carrying out the invention are selected from the group consisting of:
(a) monoesters of hydroxybenzoic acid and hydroxynaphthoic acid of the formula (A)
wherein R is C
1
-C
8
alkyl, benzyl, phenyl or naphthyl; Ar is substituted or unsubstituted phenylene or naphthylene; or formula (AA) where M is a cation such as, but not limited to, sodium, ammonium, tetraalkyl ammonium, potassium, calcium, magnesium or zinc;
(b) diesters of hydroxybenzoic acid of the formula (B)
wherein Ar is as defined above, and R
1
is C
1
-C
8
alkyl, (CH
2
CH
2
O)
k
CH
2
CH
2
where k is 1 or more, benzyl, phenyl or naphthyl; or formula (BB) where M is as defined above.
(c) monoamides of hydroxybenzoic acid and hydroxynaphthoic acid of the formula (C)
wherein R and Ar are as defined above; or formula (CC) where M is as defined above.
(d) diamides of hydroxybenzoic acid of the formula (D)
wherein Ar is as defined above, and R
2
is C
1
-C
8
alkyl, (CH
2
CH
2
O)
k
CH
2
CH
2
where k is 1 or more, benzyl, phenyl or naphthyl; or formula (DD) where M is as defined above.
(e) ester-amides of hydroxybenzoic acid of the formula (E)
where Ar is as defined above and R
3
is C
1
-C
8
alkyl, C
1
-C
8
dialkyl, (CH
2
CH
2
O)
k
CH
2
CH
2
, where k is 1 or greater, benzyl, phenyl or naphthyl, or formula (EE) where M is as defined above.
The above-defined barrier-enhancing additives can be obtained from commerc
D'Arcangelis Samuel Tacitus
Ford Thomas Michael
Plotzker Irene Greenwald
Sharp Kenneth George
E. I. du Pont de Nemours and Company
Krukiel Charles E.
Michl Paul R.
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