Stabilizer combination for the rotomolding process

Details Stabilizer combination for the rotomolding process Stabilizer combination for the rotomolding process

1999-12-06

2002-09-03

Mulcahy, Peter D. (Department: 1713)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

Processes of preparing a desired or intentional composition...

C524S128000, C264S209200, C264S310000, C264S312000

Reexamination Certificate

active

06444733

ABSTRACT:

The present invention relates to the production of polyolefin hollow articles by the roto-molding process, the processing stabilizer combination described hereinbelow being used.
The rotomolding or rotational molding/casting process is used for the production of fairly large plastic hollow articles which may be reinforced with glass fibres (Encyclopedia of Polymer Science and Engineering, Wiley Interscience, 1988, Vol. 14, pages 659-670). In principle, this process is carried out as follows: The plastic material is filled into one half of the mold which is then closed with the other half and heated in an oven such that the fused plastic material spreads to the walls of the mold when rotated around different axes. The hollow article is obtained after cooling. In this manner it is possible to produce, for example, storage and truck tanks from HD polyethylene. The process normally requires temperatures in the range above 300° C., sometimes even above 400° C. The requirements placed on the stabilizers are therefore different from and more stringent than those, for example, of the extrusion process where the temperatures are normally not much above 280° C.
The use of stabilizer combinations of phosphites or phosphonites with sterically hindered phenols and/or sterically hindered amines (HALS) in polyolefins is known [see, inter alia, R. Gächter, H. Müller, “Plastics Additives Handbook”, Hanser Publishers, pages 40-71 (1990)].
Hydroxylamine derivatives, such as N,N,-dialkylhydroxylamines and N,N-dibenzylhydroxylamine, are well known as useful stabilizers for a variety of polymeric substrates as is taught for example in U.S. Pat. Nos. 4,590,231, 4,668,721, 4,782,105 and 4,876,300, the relevant parts of which are incorporated herein by reference.
U.S. Pat. Nos. 4,649,221, 4,691,015 and 4,703,073 teach the use of polyhydroxylamine compounds, hydroxylamines derived from hindered amines and alkylated N,N-dibenzylhydroxylamine derivatives, respectively, with one or more compounds selected from the group of phenolic antioxidants, hindered amine light stabilizers, alkylated hydroxybenzoate light stabilizers, ultraviolet light absorbers, organic phosphorus compounds, alkaline metal salts of fatty acids and thiosynergists towards stabilizing polyolefins.
U.S. Pat. No. 4,782,105 discloses the use of long chain N,N-dialkylhydroxylamines for the stabilization of poly(arylene sulfides) and unsaturated elastomers. Examples are shown where long chain N,N-dialkylhydroxylamines are used together with phosphite stabilizers in styrene/butadiene copolymer.
U.S. Pat. No. 4,876,300 discloses the use of long chain N,N-dialkylhydroxylamines as process stabilizers for polyolefin compositions. Examples are shown where long chain N,N-dialkylhydroxylamines are used together with phosphite stabilizers and also where they are used together with hindered amine stabilizers.
U.S. Pat. Nos. 4,590,231 and 4,668,721 disclose the use of N,N-dibenzylhydroxylamine or other hydroxylamine derivatives together with metal salts of fatty acids and phenolic antioxidants for the stabilization of polyolefin compositions. The compositions may also contain organic phosphorus compounds or hindered amine stabilizers.
U.S. Pat. No. 5,013,510 teaches a process for the preparation of long-chain N,N-dialkylhydroxylamines by direct oxidation. It is mentioned that the long-chain N,N-dialkylhydroxylamines are effective towards stabilizing polyolefin compositions.
U.S. Pat. No. 5,596,033 discloses the stabilization of polypropylene fiber with a binary system of select hindered amines with the N,N-dialkylhydroxylamine produced by the direct oxidation of N,N-di(hydrogenated tallow)amine.
U.S. Pat. No. 5,149,774 discloses the use of hydroxylamine derivatives towards reducing color formation during the recycling of already discolored polyolefin resins.
U.S. Pat. Nos. 5,844,029 and 5,880,191 disclose the use of saturated hydrocarbon amine oxides towards the stabilization of thermoplastic resins. It is disclosed that the thermoplastic compositions may further contain a stabilizer or mixture of stabilizers selected from phenolic antioxidants, hindered amine light stabilizers, ultraviolet light absorbers, organic phosphorus compounds, alkaline metal salts of fatty acids and thiosynergists. The co-use of amine oxides with other stabilizers towards stabilizing polyolefins is not exemplified.
It has now been found that the combination of hydroxylamine derivatives, together with organic phosphites or phosphonites and hindered amine stabilizers results in excellent stabilization in the rotomolding process. The hollow articles prepared according to the present invention exhibit excellent initial color and gas fading resistance.
Accordingly, this invention relates to a novel process for the production of polyolefin hollow articles, which comprises
charging the polyolefin with a stabilizer combination, comprising
(a) at least one compound from the group of the organic phosphites and phosphonites,
(b) one or more compounds selected from the group consisting of
i.) hydroxylamine derivatives and
ii.) amine oxide derivatives and
(c) at least one compound from the group of the hindered amine stabilizers,
filling this mixture into a mold, heating this mold in an oven to above 280° C., such that the stabilized polyolefin fuses,
rotating the mold around at least 2 axes, the plastic material spreading to the walls,
cooling the mold while still rotating,
opening it, and
taking the resultant hollow article out.
Of interest is a novel process wherein component (a) is at least one compound selected from the formulae (1), (2), (3), (4), (5), (6) and (7)
in which the indices are integral and
n is 2, 3 or 4; p is 1 or 2; q is 2 or 3; r is 4 to 12; y is 1, 2 or 3; and z is 1 to 6;
A
1
, if n is 2, is C
2
-C
18
alkylene; C
2
-C
12
alkylene interrupted by oxygen, sulfur or —NR
4
—; a radical of the formula
or
phenylene;
A
1
, if n is 3, is a radical of the formula —C
r
H
2r−1
—;
A
1
, if n is 4, is
A
2
is as defined for A
1
if n is 2;
B is a direct bond, —CH
2
—, —CHR
4
—, —CR
1
R
4
—, sulfur, C
5
-C
7
cycloalkylidene, or cyclohexylidene which is substituted by from 1 to 4 C
1
-C
4
alkyl radicals in position 3, 4 and/or 5;
D
1
, if p is 1, is C
1
-C
4
alkyl and, if p is 2, is —CH
2
OCH
2
—;
D
2
, if p is 1, is C
1
-C
4
alkyl;
E, if y is 1, is C
1
-C
18
alkyl, —OR
1
or halogen;
E, if y is 2, is —O—A
2
—O—,
E, if y is 3, is a radical of the formula R
4
C(CH
2
O—)
3
or N(CH
2
CH
2
O—)
3
;
Q is the radical of an at least z-valent alcohol or phenol, this radical being attached via the oxygen atom to the phosphorus atom;
R
1
, R
2
and R
3
independently of one another are C
1
-C
18
alkyl which is unsubstituted or substituted by halogen, —COOR
4
, —CN or —CONR
4
R
4
; C
2
-C
18
alkyl interrupted by oxygen, sulfur or —NR
4
—; C
7
-C
9
phenylalkyl; C
5
-C
12
cycloalkyl, phenyl or naphthyl; naphthyl or phenyl substituted by halogen, 1 to 3 alkyl radicals or alkoxy radicals having a total of 1 to 18 carbon atoms or by C
7
-C
9
phenylalkyl; or a radical of the formula
 in which m is an integer from the range 3 to 6;
R
4
is hydrogen, C
1
-C
18
alkyl, C
5
-C
12
cycloalkyl or C
7
-C
9
phenylalkyl,
R
5
and R
6
independently of one another are hydrogen, C
1
-C
8
alkyl or C
5
-C
6
cycloalkyl,
R
7
and R
8
, if q is 2, independently of one another are C
1
-C
4
alkyl or together are a 2,3-dehydropentamethylene radical; and
R
7
and R
8
, if q is 3, are methyl;
R
14
is hydrogen, C
1
-C
9
alkyl or cyclohexyl,
R
15
is hydrogen or methyl and, if two or more radicals R
14
and R
15
are present, these radicals are identical or different,
X and Y are each a direct bond or oxygen,
Z is a direct bond, methylene, —C(R
16
)
2
— or sulfur, and
R
16
is C
1
-C
8
alkyl.
Of particular interest is a novel process wherein component (a) is at least one compound selected from the formulae (1), (2), (5) and (6), in which
n is the number 2, and y is the number 1, 2 or 3;
A
1
is C
2
-C
18
alkylene, p-phenylene or p-biphenylene,
E, if y is 1, is C
1
-C
18
alk

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