Method of stabilizing EPDM modified polypropylene by adding...

Details Method of stabilizing EPDM modified polypropylene by adding... Method of stabilizing EPDM modified polypropylene by adding...

1998-02-17

2001-03-13

Rotman, Alan L. (Department: 1612)

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

Synthetic resins

Processes of preparing a desired or intentional composition...

C526S263000, C526S265000, C546S187000

Reexamination Certificate

active

06201047

ABSTRACT:

The invention relates to the subject-matter of the Patent claims.
The light stabilization of mouldings of EPDM-modified polypropylene in automotive construction, especially of car bumpers, is a particularly demanding task owing to the heterogeneous composition of the polymer matrix and its partial crystallinity, since (a) the migration of the light stabilizer to the surface must be prevented and (b) the light stabilization must be secured at a high level with good permanence over a long period of time.
The object of the present invention, therefore, was to stabilize EPDM-modified polypropylene, which is used in particular in automotive construction, against the effect of light.
This object is achieved, and the prior art greatly exceeded, by the present invention. It has in fact been found that the migration of the stabilizer can be prevented if it is bound chemically to the EPDM-modified polypropylene. Chemical binding to the EPDM-modified polypropylene takes place by exposing the EPDM-modified polypropylene comprising the novel stabilizer of formula I below to high-energy light, the bond to the surface of the polymer and/or within the polymer matrix being formed in layers close to the surface. Light stabilization at a high level is ensured in that the stabilizer compounds, which are located in the interior of a moulding produced from EPDM-modified polypropylene comprising novel stabilizer compounds, diffuse slowly to the surface where they are bound chemically to the EPDM-modified polypropylene by the exposure which occurs in the course of service. Thus any destroyed stabilizer compounds are immediately replaced at the surface and the high permanence of the UV stabilization is maintained.
The invention therefore provides for the use of piperidine compounds of the formula I
in which
R
1
is hydrogen, hydroxyl, lower alkyl, lower alkoxy, acyl or oxygen
R
2
is a substituted or unsubstituted, mono- or bicyclic radical of aromatic type,
R
3
is oxygen, —NH— or —N(C
1-4
-alkyl)- and
R
8
independently at each occurrence is hydrogen or methyl
for producing light-stabilized, EPDM-modified polypropylene which is employed in particular in automotive construction, such as for shock absorbers, cover strips and the like.
By lower alkyl are meant preferably radicals having 1-8, especially 1 or 2, carbon atoms; suitable acyl radicals are preferably those of formic, acetic or propionic acid.
All radicals R
1
are preferably hydrogen, hydroxyl, methyl or C
1-8
-alkoxy, especially hydrogen or methyl, in particular methyl.
Examples of suitable mono- or bicyclic radicals R
2
of aromatic type are benzene, naphthalene and nitrogen- and/or sulphur-containing five- or six-membered rings with or without a fused-on benzene ring which carry, for example, sterically hindered hydroxyl as substituents (3,5-di-tert-butyl-4-hydroxyphenyl), or a thienyl radical. Aromatic six-membered rings are preferred. Examples of possible substituents on these rings are hydroxyl, lower alkyl or alkoxy, preferably methyl, tert-butyl, methoxy, ethoxy, hydroxyl and one or two further groups of the formula
Every R
8
is preferably hydrogen.
Additional stabilizers which can be employed for the EPDM-modified polypropylene include antioxidants, for example sterically hindered phenols, secondary aromatic amines or thioethers (described, for example, in “Plastics Additives”, Gachter and Muller, 1985, pp. 8-12), further HALS compounds, antistatic agents, flame retardants, plasticizers, nucleating agents, metal passivators, biocides and the like.
The invention also provides for the combination of piperidine compounds of the formula I with known UV absorbers (2-(2′-hydroxyphenyl)benzotriazole compounds, 2-hydroxybenzotriazole compounds, 1,3-bis(2′-hydroxy-benzoyl)benzenesalicylates, cinnamic acid derivatives, triazine derivatives and oxalanilides). It has been found that by mixtures of compounds of the formula I and UV absorbers in a ratio of from 10:1 to 1:10, preferably from 4:1 to 1:4, depending on the thickness of the article to be stabilized, the equilibrium between diffusion rate and photochemical binding of stabilizers of the formula I to the polymer matrix can be influenced and thus the light stabilization effect improved.
The following compounds of the formulae Ia and Ib are particularly suitable for the light stabilization of EPDM-modified polypropylene:
in which
R
4
═H, OCH
3
R′
1
═H, CH
3
, OC
8
H
17
(n),
and
in which
R″
1
═H, CH
3
.
Chemical binding to the EPDM-modified polypropylene takes place during service and thus in the course of exposure of the EPDM-modified polypropylene comprising the novel piperidine compound to high-energy visible or near UV light, the period of exposure necessary for this generally being between about 100 and 400 hours. Exposure can take place with a xenon lamp or with sunlight. Under such exposure, the double bonds in the compound of the formula I are broken and chemical bonding takes place to appropriately reactive carbon atoms of the EPDM-modified polypropylene.
In the case of bulky mouldings such as car bummers, the HALS compounds in the interior of the mouldings (that is, the piperidine compounds or piperidine radicals which act as stabilizer) will diffuse slowly towards the surfaces where they are bound chemically to the EPDM-modified polypropylene as a result of the exposure which occurs in the course of service. In this way, any destroyed HALS stabilizers at the surface are continually replaced and stabilization is extended for a substantially longer time.
In general use is made of from 0.05 to 2.5%, preferably from 0.1 to 0.6k, of one or more compounds of the formula I, based on the weight of the EPDM-modified polypropylene to be stabilized and depending on the target level of stabilization or on the service life (1, 2 or 10 years) or geographical area of deployment of the finished polymer article.
Polymer articles which have been stabilized in accordance with the present invention against the damaging effect of UV light have the feature, not found in the prior art, that after only a short period of service and thus of exposure to light it is no longer possible to remove the stabilizers (compounds of the formula I) from the EPDM-modified polypropylene by physical means, even by eluting with solvents. With the conventional use of the polymer articles the leaching, i.e. the loss of stabilizers, can be attributed to climatic and/or environmental influences (for example, contact with cleaning liquids, oils, fats or other chemicals). Even under these conditions the polymers UV-stabilized in accordance with the invention exhibit a high resistance. In general, EPDM-modified polypropylene with a basic level of stabilization is employed as the base material and is UV-stabilized in accordance with the invention in a second processing step. Basic stabilization is generally carried out, as is known, with 0.05-0.2% of a phenolic antioxidant and 0.05-0.5% of calcium stearate, based on the weight of the EPDM-modified polypropylene.
The preparation of compounds of the formula I [likewise those of the formula (Ia) and (Ib)] is known and takes place by condensation of one mole of the compound of the formula II
R
2
—CH═C═(COOH)
2
  (II)
or of a functional acid derivative, for example a low molecular mass ester or an acid halide, with 2 mol of a compound of the formula III
In the examples below the parts and percentages are by weight. The parts by volume correspond to the volume of equal parts by weight of water. The temperatures are indicated in degrees Celsius.
I. Preparing compounds of the formula I


REFERENCES:
patent: 5021478 (1991-06-01), Ravichandran et al.
patent: 5705545 (1998-01-01), Avar et al.
patent: 3412227 (1984-11-01), None

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