Stock material or miscellaneous articles – Hollow or container type article – Polymer or resin containing
Reexamination Certificate
2000-07-31
2002-09-03
Woodward, Ana (Department: 1711)
Stock material or miscellaneous articles
Hollow or container type article
Polymer or resin containing
C525S425000
Reexamination Certificate
active
06444283
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
This invention relates to polyester/polyamide blends having low haze and reduced gas permeability properties compared to the polyester alone. More specifically, this invention relates to blends of a semi-crystalline polyester such as poly(ethylene terephthalate) (PET) with low molecular weight high permeability polyamides where significantly reduced gas permeability (over neat PET) is obtained with a low level of haze. These low haze and reduced gas permeability polyester/polyamide blends have practical applications in containers and packages for food, beverages, cosmetics, pharmaceuticals and personal care products that can be fabricated from the blends.
BACKGROUND OF THE INVENTION
Many polyamides are known in the art to possess excellent gas barrier properties. A particularly useful polyamide with high barrier is poly(m-xylylene adipamide), known commercially as MXD6 and produced by Mitsubishi Gas Chemical (Harada, M., Plastics Engineering, Jan. 27, 1998). MXD6 is a high molecular weight polyamide and has found useful applications in multilayer containers, as the middle high barrier layer in trilayer configurations. There are previous disclosures related to polyamide/PET blends that exhibit enhanced gas barrier properties over PET. For example, U.S. Pat. No. 4,501,781 discloses oriented hollow blow-molded containers comprising a mixture of PET and a xylylene group containing polyamide resin where this mixture of polymers is used as a barrier layer in a multilayer configuration so that “high bonding strength” between the layers is maintained. This patent discloses that these blends have “relatively high transparency” and that containers with a high degree of transparency can be provided. It also discloses that compositions having as close to 30% of the xylylene group-containing polyamide resin to PET as possible are necessary for “high gas barrier properties.” Furthermore, this patent states that the use of 5-10% by weight of the xylylene group-containing polyamide resin to PET will result in a container that does not have high gas barrier properties. U.S. Pat. No. 5,314,987 discloses blends of MXD6 with polyesters that have been made with catalyst systems that do not contain Co or Mn. The clarity of these blends was said to be enhanced by the addition of Co octoate.
Blends of high molecular weight polyamides, such as MXD6 with PET, are known to have high haze values which limits their use in practical food packaging container applications. However, the use of low molecular weight polyamides has been found to be particularly useful in reducing the haze values in polyester/polyamide blends. U.S. Pat. No. 5,258,233 and 5,266,413 teach that the use of partially aromatic polyamides with number average molecular weights of less than 15,000, at concentrations less than 2.0 wt. %, are useful in preparing high clarity, low haze blends with PET for the reduction of acetaldehyde. Haze values of higher molecular weight polyamides were demonstrated in these patents to be too high for practical use.
Current theories for the enhanced gas barrier properties exhibited when a high molecular weight polymer is blended with a high barrier polymer are based on the development of distinct layered or platelet like morphologies formed from the high barrier component during processing. In order for this kind of deformation, etc. to occur, it has been generally accepted that the high barrier polymer must be at relatively high molecular weight in order to respond to the external mechanical forces in the processing step (G. W. Lohfink and M. R. Kamal,
Polymer Engineering and Science
, 1993, 33 (21) 1404).
U.S. Pat. No. 5,866,649 teaches that blend compositions of PET and up to about 30% of a xylylene group-containing polyamide have superior barrier and oxygen absorption properties under certain conditions when a transition metal catalyst is present in the blend and the material has been biaxially oriented. The reference also teaches that in oriented blends spherules of barrier material become elongated biaxially, thereby increasing their surface area substantially.
None of the references disclose polyester/low molecular weight polyamide blends having low haze and reduced gas permeability properties that are equivalent to polyester/high molecular weight polyamide blend compositions.
SUMMARY OF THE INVENTION
The present invention provides for polyester/polyamide blend compositions, methods of making and articles of manufacture.
In one embodiment, the invention provides a polymer blend comprising:
I. from about 80 to about 99.5 weight % of a semi-crystalline polyester, which comprises the residues of
(A) a dicarboxylic acid component comprising repeat units from at least about 85 mole % of terephthalic acid, naphthalene-2,6-dicarboxylic acid or a mixture thereof; and
(B) a glycol component comprising repeat units from at least about 85 mole % ethylene glycol, based on 100 mole % dicarboxylic acid and 100 mole % glycol; and
II. from about 20 to greater than about 2 weight % of a low molecular weight polyamide, having a number average molecular weight of less than about 15,000, having the repeating unit A-D, wherein A is the residue of a dicarboxylic acid comprising adipic acid, isophthalic acid, terephthalic acid, 1,4-cyclohexanedicarboxylic, resorcinol dicarboxylic acid, or naphthalenedicarboxylic acid, or a mixture thereof, and D is a residue of a diamine comprising m-xylylene diamine, p-xylylene diamine, hexamethylene diamine, ethylene diamine, or 1,4-cyclohexanedimethylamine, or a mixture thereof.
In another embodiment, the invention provides a method for reducing gas permeability of polyester comprising blending:
I. from about 80 to about 99.5 weight % of a semi-crystalline polyester, which comprises the residues of:
(A) a dicarboxylic acid component comprising repeat units from at least about 85 mole % of terephthalic acid, naphthalene-2,6-dicarboxylic acid or a mixture thereof; and
(B) a glycol component comprising repeat units from at least about 85 mole % ethylene glycol, based on 100 mole % dicarboxylic acid and 100 mole % of glycol; and
II. from about 20 to greater than about 2 weight % of a low molecular weight polyamide having a number average molecular weight of less than about 15,000 having the repeating unit A-D, wherein A is the residue of a dicarboxylic acid comprising adipic acid, isophthalic acid, terephthalic acid, 1,4-cyclohexanedicarboxylic, resorcinol dicarboxylic acid, or naphthalenedicarboxylic acid, or a mixture thereof, and D is the residue of a diamine comprising m-xylylene diamine, p-xylylene diamine, hexamethylene diamine, ethylene diamine, or 1,4-cyclohexanedimethylamine, or a mixture thereof.
Additional advantages of the invention will be set forth in part in the detailed description, which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The advantages of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the appended claims. It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory of preferred embodiments of the invention, and are not restrictive of the invention, as claimed.
DETAILED DESCRIPTION OF THE INVENTION
The invention relates to a polyester/polyamide blend having low haze and reduced gas permeability properties comprising a semi-crystalline polyester and a low molecular weight polyamide having a number average molecular weight of less than about 15,000. Contrary to current theories, the polyester/low molecular weight polyamide blends not only have reduced acetaldehyde levels, but also have low haze and reduced gas permeability levels that are equivalent to high molecular weight polyamide/PET blends. The present polyester/polyamide blends may be processed and molded into a shaped article.
The present invention may be understood more readily by reference to the following detailed description of the invention and the e
Connell Gary Wayne
Hewa John David
Stafford Steven Lee
Turner Sam Richard
Carmen, Esq. Dennis V.
Eastman Chemical Company
Graves, Jr. Esq. Bernard J.
Woodward Ana
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