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
2001-05-30
2002-10-08
Szekely, Peter (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...
C524S368000, C524S381000, C524S392000
Reexamination Certificate
active
06462116
ABSTRACT:
BACKGROUND OF THE INVENTION
Halogen containing polymers, especially those containing chlorine, are used widely and have great commercial significance. Polyvinyl chloride (PVC), in particular, is used in packaging, siding, pipe, and many extruded shapes. Such large scale and diverse use of the halogen-containing polymers depends upon the incorporation therein of good heat and light stabilizers. PVC, for example, is known to have a tendency to degrade upon prolonged exposure to heat and light during processing and use. Darkening or other color change and the loss of tensile, flexural, and impact strengths are the results of such degradation. Unless good low-cost stabilizers are available for addition to the polymer composition, the service life of articles made from the composition is limited, and its use severely restricted, as will be the conditions for making it.
One particularly troublesome form of degradation occurs when the polymer composition is processed into articles by methods employing heat to melt or soften the polymer. A color change can occur during the first few minutes at high temperatures (e.g., from about 175 to about 200° C.) and it is commonly referred to as early color or early discoloration. The avoidance of such early color is notably important in the manufacture of plastic pipe and siding. It is, of course, also important to prevent or reduce discoloration and deterioration of the polymer during extended exposure to high temperatures, which can lead to sudden and catastrophic degradation into a pitch-like abrasive material and cause the formation of corrosive materials such as HCl inside the fabricating equipment. The inner, highly polished surfaces of the equipment can thus be rendered essentially useless. A particularly troublesome instance of such sudden degradation often occurs when zinc compounds are employed as stabilizers; the phenomenon is known as “zinc burn” in the PVC industry.
An example of zinc burn is illustrated in U.S. Pat. No. 4,515,916, wherein a PVC composition containing zinc bis-(octyl thioglycolate) and a substituted dihydropyridine as a co-stabilizer showed such burn after 3 minutes on a two roll mill at 193° C.
In U.S. Pat. No. 3,417,039, Penneck teaches a stabilizing composition for chlorine-containing polymers which comprises a zinc salt of a carboxylic acid which may have sulfur substituents, a polyhydric alcohol, and an organic sulfur-bearing compound having the formula R
1
-S
(1-2)
-R
2
, which is exemplified by bis-(n-dodecyloxyethyl) sulfide. The suitable salt-forming acids include benzoic, salicylic, phthalic, and maleic acid. Zinc 2-ethylhexyl maleate is a preferred salt. As shown hereinbelow, Penneck's stabilizing composition does not overcome the zinc burn problem.
In U.S. Pat. No. 4,963,594, noting that although innumberable sulfur compounds are said to be useful as heat stabilizers for PVC it is very difficult to select those which do in fact exert a heat stabilizing influence, Gay teaches a combination of a thiomalic ester such as 2-ethylhexyl thiomalate, an organozinc derivated such as the zinc mercaptide of isooctyl 2-mercaptoacetate, and an organic derivative of a metal from Group IIa of the Periodic Table such as calcium stearate.
British Patent No. 936,770 teaches that a PVC stabilizer comprising a synergistic combination of a terpene such as &bgr;pinene, a thio compound such as thioglycerol or an alkyl mercaptopropionate, and a zinc mercaptoester provides an extraordinarily high degree of stabilization. It teaches that such compositions are uniquely suitable for commercially advantageous high speed, high temperature forming operations such as melt extrusion.
Now, we have discovered that certain organothio compounds are superior co-stabilizers in combination with the zinc bis(mercaptoacid esters) when present during high temperature processing of halogen-containing polymers such as PVC.
SUMMARY OF THE INVENTION
It is an object of this invention to provide an improved heat stabilizer for halogen-containing polymer compositions.
It is an object of this invention to provide a halogen-containing polymer composition having improved heat stability.
It is a related object of this invention to eliminate zinc bum during the processing of pvc compositions at elevated temperatures.
These and other objects which will become apparent from the following description are achieved by a composition consisting essentially of a halogen-containing polymer and a stabilizer composition comprising:
(A) an organothio compound selected from the group consisting of a dithiodiglycol, and polyformals and polyacetals of said dithiodiglycol; and a mercaptoalkanol having the formula
wherein R
1
and R
2
are the same or different and are hydrogen or C
1
to C
18
alkyl; and i is 0 or an integer from 1 to 6 inclusive;
at least one zinc mercaptoester selected from the group consisting of
(B
1
) a zinc mercaptoacid ester having the formula:
Zn—[S(CH
2
)
x
—C(═O)OR]
2
,
wherein R is a hydrocarbyl radical having from 2 to about 22 carbon atoms and x is 1 or 2;
(B
2
) a zinc mercaptoacid ester having the formula:
Zn—[S(CHR′)
a
(CH
2
)
b
—[C(═O)O]R″]
2
;
wherein
R′ is methyl or C(═O)OR″;
R″ is [(CH
2
—[C—(R*)(R
2
*)]
y
CH
2
O)
z
R
3
*];
R* is H, alkyl, or hydroxyalkyl;
R
2
* is OH, hydroxy-substituted alkyl, or O(O═)C—R
4
*;
R
3
* is H, (O═)C—R
4
*, or alkyl,
R
4
* is alkyl or alkenyl;
a=0 or 1; b=1 or 2; y=0 or 1; and z=1 to 4; with the proviso that when z is greater than 1, y=0; and
(B
3
) a zinc mercaptoalkyl carboxylic acid ester having the formula:
Zn [SCH
2
(CH
2
)
q
O—C(═O)R
5
* ]
2
wherein
R
5
* is an alkyl or alkenyl group having from 1 to 18 carbon atoms or an aryl group having from 6 to 12 carbon atoms, and q is from 1 to 6;
(C) from 0 to 40 phr of a basic alkali or alkaline earth metal compound; and
(D) from 0 to 40 phr of a substituted dihydropyridine
DETAILED DESCRIPTION OF THE INVENTION
Examples of the mercaptoalkanols include without limitation mercaptoethanol, mercaptopropanol, mercapto iso-propanol, and mercapto iso-undecanol.
Dithiodiglycol and polyformals and polyacetals thereof having the formula:
H—(OCH2CH2SSCH2CH2OCR
2
)
n
—OH
wherein R is hydrogen or methyl and n is 3-12 are among the preferred organic sulfides for the purposes of this invention.
The zinc mercaptoesters of Formula B
1
are exemplified by zinc bis(2-ethylhexylthioglycolate), zinc bis(octylmercaptopropionate), zinc bis(octadecylthioglycolate), zinc bis(octadecylmercaptopropionate), and zinc bis(ethylthioglycolate). They are easily prepared by the reaction of the corresponding mercaptoacid ester with zinc chloride in the presence of a suitable hydrogen chloride scavenger such as ammonia, ammonium hydroxide, and an alkali metal hydroxide or a carbonate thereof. Another method is the condensation of the mercaptoacid ester with zinc oxide in an organic medium such as a high boiling naphtha, xylene, paraffin wax and the like. Any ratio of the zinc compound and the mercaptoester will suffice so long as the reaction conditions are such as to drive the condensation but it is preferred to use a stoichiometric ratio of the reactants. Atmospheric pressure is suitable but the reaction will proceed satisfactorily at from about 50 to about 80° C. under reduced pressure. The maximum temperature is about 140-150° C.
The zinc bis-mercaptoacid ester may also be selected from among those disclosed in U.S. Pat. No. 5,536,767 including the zinc bis-thioglycolate, zinc bis-mercaptopropionate, and zinc mercaptosuccinate of a polyhydric alcohol or ether, carboxylate, or ether-carboxylate thereof having at least one functional hydroxy group as exemplified by ethylene glycol, glycerol, tetraethylene glycol, trimethylolethane, pentaerythritol, glycol ethers such as tetraethylene glycol monobutyl ether, and diethylene glycol monoethyl ether, glycol mono-carboxylates such as diethylene glycol monocaprate and ethyle
Beekman George F.
Mesch Keith A.
Price Lionel R.
Morton International Inc.
Szekely Peter
LandOfFree
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