Stabilizer composition

Details Stabilizer composition Stabilizer composition

1997-04-10

2003-07-15

McKane, Joseph K. (Department: 1266)

Organic compounds -- part of the class 532-570 series

Organic compounds

Phosphorus esters

C252S400400

Reexamination Certificate

active

06593485

ABSTRACT:

This invention relates to a stabilizer composition comprising at least one processing stabilizer selected from special phosphite and mono- and diphosphonite compounds, at least one acid scavenger selected from the group consisting of selected metal stearates, hydrotalcites, oxides and hydroxides of alkaline earth metals, at least one UV stabilizer selected from compounds containing at least one 2,2,6,6-tetraalkylpiperidinyl group and, optionally, at least one sterically hindered phenolic antioxidant. The invention relates also to a solid masterbatch composition or a liquid concentrate comprising an above-mentioned stabilizer composition. The invention further relates to a process for stabilizing polymeric materials selected from the group consisting of special polyolefins comprising adding to the polymeric material a stabilizing quantity of said stabilizing composition. The invention also relates to stabilized polymeric material comprising said stabilizer composition and the above-mentioned polymeric material.
The rapid progress in the development of polymerization catalysts, especially supported catalysts and metallocenes, for the manufacture of polyolefins has made a variety of polymers available which differ significantly in their properties from the “early generation” plastics. The problem to maintain these superior properties during processing and service life of the plastic articles has been aggravated especially in polyolefins produced by Generation II to V catalyst systems which are not removed from the polymer after finalizing the polymerization reaction. Even though such catalysts can be deactivated by catalyst poisons, such as steam, aliphatic alcohols, ethers or ketones, their residual activity can still remain to a certain extent. They can attack the polymer and cause premature failures during its end-use; and furthermore, such catalyst residues can also affect the additives which are supposed to safeguard the integrity of plastic materials.
It is well known that several cations with a positive charge ≧2, especially transition metal ions of the 3d, 4d, and 5d series—typical catalysts for olefin polymerization—, can catalyze the decomposition of phosphites and phosphonites, in particular the hydrolysis of such typical processing stabilizers, finally leading to products with acidic properties and also undesired free phenol. These decomposition products as such can, moreover, cause many disadvantageous secondary effects; for example negative interactions with other additives, especially hindered amine UV stabilizers and phenolic antioxidants, eventually disturbing the entire balance of the additive system contained. In consequence thereof, problems can become apparent already during melt processing of the polymer, e.g. in the form of gel particles, various kinds of deposits or black specks, as well as during its service life, e.g. as reduced mechanical properties, surface cracks or premature embrittlement, when the polymer is exposed to daylight or climate influences.
Many of these undesired processes in a polymeric matrix have been found to originate from a certain acidity, originally present or later formed during the lifetime of a polymer. Therefore, sufficient amounts of acid scavengers, such as metal stearates or oxides, are added to overcome the aforementioned problems. One of the most widely used acid scavengers is calcium stearate, typically used in concentrations of 0.03-0.15%.
However, several other undesired processes, which cannot directly be correlated with the formation of acidity, have been observed in a polymeric matrix despite the presence of acid scavengers. Although the details of such reactions or mechanisms are not fully understood, the consequences thereof can become clearly visible. For instance, certain combinations of plastic additives appear to show negative interactions, often expressed as reduced overall performance, compared with the individual effects of the single additives applied alone in the same polymer.
One example of such negative interactions is the simultaneous use of certain processing stabilizers, e.g. SANDOSTAB P-EPQ or IRGAFOS 12, together with sterically hindered amines (HALS) in UV stabilized polyolefins. Both types of additives are commercially, respectively from a technical viewpoint, important products and essential for the use in high performance plastics. The phosphorus compounds are known to exceptionally safeguard the integrity of the polymer during melt processing; HALS compounds are the state-of-the art stabilizers to protect polyolefins against the detrimental influence of UV light. However, these two types of additives are known to interact antagonistically and, therefore, it has been explicitly recommended not to use any combinations thereof (See publication of Dr. W. O. Drake of Ciba-Geigy, Basel in “Plastics News”, April 1989, pages 36-45.) In particular, the efficiency of HALS as UV stabilizers is said to be drastically reduced in such cases, limiting the industrial use of such combinations significantly.
It is the objective of the invention to solve the above-mentioned and to provide a high performance stabilizer composition for the stabilization of polyolefins, in particular those which are produced by Generation II to V (or higher) catalyst systems which are not removed from the polymer after the polymerization reaction.
In accordance with the present invention said problem is solved by a stabilizer composition comprising
a) at least one processing stabilizer selected from the group consisting of phosphite, monophosphonite and diphosphonite compounds of formula I or II
 in which
m is 0 or 1;
n is 0 or 1;
each R
10
and each R
11
, independently, is an aliphatic, alicyclic or aromatic group of 1 to 24 carbon atoms, optionally further substituted (for example by linear or branched aliphatic groups or alkaryl substituents) (hereinafter defined as the monovalent significances of R
10
or R
11
, respectively);
or both groups R
10
and/or R
11
form a cyclic group with a single phosphorus atom (hereinafter defined as the divalent significances of R
10
or R
11
, respectively);
Y is —O—, —S—, —CH(R
15
)— or —C
6
H
4
—;
where R
15
is hydrogen or C
1-6
alkyl or COOR
6
and R
6
is C
18
alkyl,
b) at least one acid scavenger selected from the group consisting of sodium stearate, magnesium stearate, zinc stearate; magnesium or magnesium/zinc hydrotalcites, optionally coated with 5 to 50% of metal stearate; zinc oxide, zinc hydroxide, calcium oxide, calcium hydroxide, magnesium oxide and magnesium hydroxide,
c) at least one UV stabilizer selected from compounds containing at least one 2,2,6,6-tetraalkylpiperidinyl group and
d) optionally at least one sterically hindered phenolic antioxidant selected from the group consisting of octadecyl-3-(3′,5′-di-tert.-butyl-4′-hydroxyphenyl)propionate, tetrakis[methylene-3-(3′5′-di-tert.-butyl-4′-hydroxyphenyl)propionate]methane, 1,3,5-trimethyl-2,4,6-tris(3,5-di-tert.-butyl-4-hydroxyphenyl)benzene, 1,3,5-tris(3,5-di-tert.-butyl-4-hydroxyphenyl)-1,3,5-triazine-2,4,6-(1H,3H,5H)trione and tris[3,5-di-tert.-butyl-4-hydroxybenzyl]isocyanurate.
According to the invention, there is provided a synergistic additive package, i.e. a stabilizer composition for polyolefins, in which highly effective processing stabilizers and hindered amine UV stabilizers are combined without sacrificing the individual effects of the additives contained. The selected acid scavengers are able to compensate the negative interactions of processing stabilizers and HALS compounds. In some cases, even superior efficiency of the HALS compounds has been observed, compared with analogous formulations containing such processing stabilizers, which do not show such negative interactions.
Preferably, in component a) the monovalent significances of R
10
and R
11
are independently linear, branched or cyclic C
1-24
aliphatic groups; or aromatic groups, e.g. phenyl, preferably substituted 1 to 5-fold with C
1-12
alkyl or aralkyl groups, as for example with R

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