Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – From carboxylic acid or derivative thereof
Reexamination Certificate
2000-12-06
2002-01-29
Boykin, Terressa M. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
From carboxylic acid or derivative thereof
C528S272000
Reexamination Certificate
active
06342578
ABSTRACT:
BACKGROUND OF THE INVENTION
1) Field of the Invention
The present invention concerns a copolyester resin having a high number of carboxyl end groups (CEG) and a method of making such a resin. Specifically, the copolyester is polyethylene terephthalate and a dicarboxylic acid, along with an anhydride resulting in a high content CEG resin characterized by reduced stress cracking. The copolyester is employed for a packaging resin useful in such as a soft drink beverage bottle, for example, with significantly improved stress cracking resistance. More particularly, the present invention also concerns a method of producing the copolyester by introducing at the end of polycondensation, one or more of phthalic anhydride, glutaric anhydride, benzoic anhydride, maleic anhydride or succinic anhydride in an amount sufficient to significantly reduce the caustic stress cracking.
2) Prior Art
Copolyester bottle resin is well known in the art. Typical copolyester bottle resins employ polyethylene terephthalate (PET) and a dicarboxylic acid such as isophthalic acid. The dicarboxylic acid was added to adjust the rate of crystallization of PET by decreasing it, in order to obtain clear bottle/jar preforms, which are stretch-blow molded into containers, such as soft drink bottles. If a crystallization retarding agent is not employed, crystallization of the preform occurs resulting in a hazy preform and a hazy bottle/jar. However, if too much dicarboxylic acid is used, the physical properties of copolyester resin are significantly weaker than PET resin.
Later, it was observed that an increase in isophthalic acid improved barrier properties of the bottle/jar of the copolyester resin. A balance in the amount of dicarboxylic acid employed was necessary to add a sufficient amount to adjust the rates of crystallization to avoid haze and improve the barrier properties, but avoid significantly weakening the copolyester (compared to PET resin).
It was then realized that the smaller (e.g. 20 ounce) soft drink beverage bottles, which have a larger volume/surface area ratio, require a higher barrier property than (2 liter) bottles. Thus the resin composition for smaller soft drink bottles contains more isophthalic acid to improve the barrier properties, than larger bottles.
The increase in isophthalic acid in copolyester resins has led to somewhat weaker physical properties especially for the smaller soft drink bottle. This weakening is observed in bottle failure from stress cracking, a problem not known before the significant increase in isophthalic acid. Stress cracking occurs over time, generally in the base of the bottle, causing a bottle under pressure with carbonated liquid to either lose pressure, or in the extreme, burst. Stress cracking can be initiated by the alkaline lubricants used in the bottle filling lines, or by the residues of alkaline cleaning solutions on store shelves.
U.S. Pat. No. 3,051,212 to Daniels; U.S Pat. No. 4,016,142 to Alexander et al.; and U.S. Pat. No. 4,442,058 to Griffith et al. teach reducing the amount of CEG present in polyester in order to increase the hydrolytic stability. More specifically, these references recognize that an increase in the CEG content for polyester, decreases the hydrolytic stability of the polymer, such that the IV stability during drying decreases, i.e., the IV drops during drying.
U.S. Pat. No. 4,328,593 to Duh discloses an amorphous polyester which has an optimal level of CEG to reduce the reaction time in a solid state polymerization vessel. Reducing the reaction time in a solid state polymerization (SSP) vessel minimizes chemical instability and deleterious polymerization byproducts. The optimum amount is defined as the amount of CEG content in the amorphous polymer necessary to react with some of the HEG (hydroxyl end groups) to favor the chemical reaction rate.
Although this reference teaches having an optimal amount of CEG during processing of the polymer, it teaches away from having an excess of CEG that remain in the resin, because such an excess would increase the SSP residence time (see FIG. 2 of the Duh reference). There is no disclosure that the polyester resin (of the preform or the blown bottle) contains a high CEG content. Polyester resin is polymer which has been solid state polymerized.
U.S. Pat. No. 4,361,681 to Bernhardt discloses PET having a reduced acetaldehyde generation rate. The PET is reacted with succinic or phthalic anhydride. The examples disclose that the anhydride was introduced by physically precoating the resin (which had been solid state polymerized) just prior to extrusion into bottle preforms. There is no disclosure relating to copolyesters or the CEG content.
U.S. Pat. No. 4,578,437 to Light et al. discloses copolyesters useful for bottle resin. Specifically, this reference discloses PET made from terephthalic acid and ethylene glycol with isophthalic acid to create the copolyester. This reference discloses its copolyesters have improved carbon dioxide barrier properties for soft drinks.
U.S. Pat. No. 5,362,844 to Kerpes et al. discloses an amorphous PET resin useful for making bottles, which has an optimum CEG content and after the PET has been SSP'd the resulting resin has a low acetaldehyde content. It is known that the CEG content in an amorphous polyester will be significantly reduced during solid state polymerization. There is no disclosure that the polyester resin, preform, or the bottle contains a high CEG content.
U.S. Pat. Nos. 5,912,307 and 6,011,132 to Paschke et al. discloses a copolyester of PET. naphthalate and/or isophthalate to increase the crystallinity of the copolyester article thereby exhibiting high carbon dioxide barrier properties.
U.S. Pat. No. 5,925,710 to Wu et al., teaches copolyesters having 2.5 weight percent of isophthalic acid. These copolyesters are useful for bottle resin. This reference discloses the amount of CEG in the amorphous resin, but does not disclose the amount of CEG in the preform or bottle (i.e., after solid state polymerization).
PCT published application WO 00/49065 to DuPont discloses a PET—isophthalic acid comonomer having a very high CEG content which was solid state polymerized for up to 24 hours. The IV never exceeded 0.639 because the HEG were essentially depleted, limiting further molecular weight enhancement. This reference also teaches that low CEG content is better for producing high IV's (see Examples 2 and 5).
To increase the SSP rate, an optimum amount of CEG in the amorphous polymer is desired as taught by the Duh patent. At the end of SSP, it is no longer desired to have free CEG within the resin and Duh states that excess CEG increase, not decrease, the SSP reaction time. It is also known that an excess of CEG in the resin has a detrimental hydrolytic stability effect (as taught by Daniels, Alexander, et al. or Griffith et al.) thus weakening and lowering its IV and producing a product having lower physical properties, compared with the physical properties obtained from a product having a higher IV. None of the references set forth above discloses stress cracking as a problem and therefore none of the references has a solution for reducing or preventing stress cracking.
It is a chief aim and object of the present invention to provide a copolyester capable of being stretch-blow molded into a bottle or jar container which exhibits improved stress cracking resistance over conventionally available polyester or copolyester resin compositions.
Likewise, it is another object of the present invention to manufacture a copolyester resin capable of being stretch-blow molded into bottles or jar containers, by making the copolyester with a high CEG content after SSP.
SUMMARY OF THE INVENTION
The resin of the present invention, directed to a copolyester of PET and at least one dicarboxylic acids such as, for example, isophthalic acid or naphthoic acid has reduced stress cracking i.e. improved stress cracking performance when small amounts of phthalic, glutaric, benzoic, maleic and/or succinic anhydride are incorporated into the copolyester. The anhyd
Arteva North America S.A.R.L.
Boykin Terressa M.
Clements Gregory N.
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