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
1996-12-20
2002-03-26
Hoke, Veronica P. (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...
C524S303000, C524S304000, C524S399000
Reexamination Certificate
active
06362264
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a composition useful for stabilizing polyvinyl chloride (PVC), especially flexible PVC formulated for food contact and medical uses. The resultant polyvinyl chloride polymers have enhanced resistance to deterioration in initial color, heat stability and clarity.
DISCUSSION OF PRIOR ART
The problem of imparting heat stability to polyvinyl chloride (PVC) at temperatures whereat the polymer becomes sufficiently fluid or softened to permit shaping is of long standing. At typical processing temperatures, PVC resins can degrade, liberating unwanted hydrogen chloride: such degraded resins can also become discolored and brittle; oftentimes they stick to the processing equipment. Degradation is commonly overcome by combining the PVC polymer, either before heating or during heat processing, with one or more heat stabilizers.
Among the more important PVC heat stabilizers in use in industry are mild alkalis such as: sodium carbonate, disodium phosphate, and sodium and potassium salts of partially esterified phosphoric acids; carboxylates and phenolates of zinc, cadmium, or alkaline earth metals have also been tried, as have inorganic and organic lead salts; other stabilizers include organotin carboxylates, as disclosed in U.S. Pat. No. 2,307,157 to Quattlebaum, and organotin mercaptides as disclosed in U.S. Pat. No. 2,641,588 to Leistner. Various metal-free organic compounds such as the polyols, e.g. mannitol, sorbitol, glycerol and pentaerythritol, organic phosphites, 1,2-epoxides, e.g. soy bean oil epoxide, isooctyl epoxystearate and the diglycidyl ether of 2,2-bis(p-hydroxyphenyl) propane, and nitrogen compounds such as phenylurea, N,N′-diphenylthiourea, and 2-phenylindole have been essayed as well.
In addition to utilizing individual stabilizers, compositions employing such materials as components have also been used. For example, U.S. Pat. No. 4,134,868 to Minagawa et al. discloses a PVC stabilizer composition comprising (A) a metal salt of a non-nitrogenous monocarboxylic acid or hydrocarbon-substituted phenol and (B) an aromatic carboxylic acid ester of a polyhydric alcohol having at least two alcoholic hydroxyls groups in its structure. This stabilizer when used alone is said to be effective in improving initial color and heat stability to the PVC resins. Further enhancement of these properties reportedly can be obtained by adding additional stabilizers such as phenols, aliphatic polyhydroxy compounds, organic phosphities, 1,2-epoxide compounds, amides and the like to the above PVC stabilizer composition.
Still another stabilizer composition for PVC resins is disclosed, for example, in U.S. Pat. No. 4,224,218 to Minagawa et al. Specifically, the '218 patent provides a PVC stabilizer composition which comprises (A) a metal salt of a sulfur- and nitrogen-free monocarboxylic acid or a phenol; and (B) a metal salt of phosphorous acid mono-ester in which the molar ratio of phosphorous acid mono-ester to metal is 1:1. Other stabilizers, such as phenols, aliphatic polyhydroxy compounds, organic phosphities, 1,2-epoxide compounds, amides and the like can also be used in conjunction with the stabilizer composition disclosed in the '218 patent to reportedly improve the overall effectiveness of the stabilizer.
A similar stabilizer composition is disclosed in U.S. Pat. No. 4,224,203 to Minagawa et al. Specifically, the stabilizer composition disclosed in the '202 patent comprises (A) a metal salt of a sulfur- and nitrogen-free monocarboxylic acid or a phenol; and (B) a metal P-hydrocarbonphosphonate having at least 1 to 30 carbon atoms in the hydrocarbon group. Such a stabilizer composition when used alone is reported to be effective in imparting improved heat resistance as well as preventing discoloration. Further enhancement of these properties is reportedly obtained by adding additional stabilizers to the stabilizer composition disclosed in the '203 patent.
U.S. Pat. No. 4,252,698 to Ito et al. provides an anti-yellowing additive for PVC resins which includes at least one overbased sulfonate or phenolate compound of lithium, sodium, potassium, magnesium, calcium, strontium, barium, zinc, titanium, aluminum, zirconium, or tin and a 1,3-diketone compound having 5 to 30 carbon atoms. Other stabilizers such as described in the '898, '218 and '203 patents may also be employed with the stabilizer composition disclosed in the '698 patent to improve the overall effectiveness of the final stabilizer composition.
Among the more common PVC stabilizers currently used are those that contain tris(nonylphenyl)phosphite, as well as other compounds related to nonylphenol. These materials have found especial utility in providing stability to flexible PVC resins. Flexible PVC resins are used in food contact environments such as packaging films and closures for bottles and jars and for medical products such as packaging for drugs and medicines, medical tubing as well as other body contact items. However, recent concerns over possible estrogenic effects attributed to stabilizers comprising nonylphenyls and related compounds has made the continued use of such stabilizers problematic.
Hence, there remains a need for developing new PVC stabilizers for use with flexible PvC resins that are used in food contact and medical contact applications which impart high heat stability and prevent discoloration of the initial PVC resin.
SUMMARY OF THE INVENTION
The present invention satisfies the aforementioned objectives and affords the other advantages described hereinbelow.
One aspect of the present invention relates to a stabilizer composition which has a low toxicity, and is capable of being used with food contact and medical contact flexible PVC polymers. Specifically, the stabilizer composition of the present invention consists essentially of (A) about 10 to about 40 parts by weight of a zinc carboxylate having the formula (RCO
2
)
2
Zn, wherein R is an aliphatic, cycloaliphatic or aromatic hydrocarbon containing from about 6 to about 22 carbon atoms; (B) about 40 to about 80 parts by weight of an alkyl ester of thiodipropionic acid having the formula S(CH
2
CH
2
CO
2
R
1
)
2
wherein R
1
is a straight chain or branched alkyl having from about 6 to about 22 carbon atoms; and (C) about 5 to about 20 parts by weight of a phenolic antioxidant such as 2,6-di-t-butyl-4-methylphenol (BHT).
The above stabilizer composition may be used alone or, optionally, with other additives well known to those skilled in the art such as epoxide compounds, inorganic stabilizers and polyhydric alcohols, i.e., polyols. It should be emphasized that these optional additives must also be low in toxicity and acceptable for food contact and medical uses. Those additives which are too toxic for such uses are excluded from the stabilizer composition of the present invention. Moreover, phosphite stabilizers such as tris(nonylphenyl)phosphite and calcium fatty acid salts such as calcium stearate are also excluded from the stabilizer composition of the present invention.
The preferred stabilizer composition of the instant invention contains FDA regulated materials and the most preferred stabilizer consists essentially of about 20 parts by weight zinc stearate; about 70 parts by weight dilaurylthiodipropionate (DLTDP); and about 10 parts by weight of BHT.
In another aspect, the present invention is directed to flexible polyvinyl chloride formulations stabilized against heat and discoloration comprising a flexible polyvinyl chloride polymer and an effective amount of the stabilizer composition of the present invention. Since the stabilizer composition of the present invention is low in toxicity, the stabilized flexible PVC resins of the present invention are highly useful as food contact products or components of medical devices.
DESCRIPTION OF THE INVENTION
As stated hereinabove, one aspect of the present invention relates to a stabilizer composition which is useful for imparting heat stability and prevent discoloration of PVC resins of the flex
CK Witco Corporation
Hoke Veronica P.
Reitenbach Daniel
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