Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
1995-03-21
2001-06-26
Reddick, Judy M. (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C106S286600, C106S287230, C106S287240, C106S287260, C106S287290, C252S400610, C252S400200, C524S108000, C524S109000, C524S126000
Reexamination Certificate
active
06251972
ABSTRACT:
The invention relates to a process for the stabilization of single-material recycled plastics, as predominantly obtained from commercial or industrial waste, and to the stabilizer mixtures which can be used for this purpose.
The recycling of waste is a problem of increasing importance for ecological reasons. The recycling of paper, textiles, glass or metals is already carried out on a large scale, whether by separate collection or by sorting of the refuse. The recycling of plastic waste and used plastics is also an increasing aim. Thermoplastics are generally processed by re-melting.
However, the plastic waste produced in the household, in commerce or in industry or the plastic materials or used plastics obtained from collections or a return obligation, for example in specific sectors of industry, such as the automobile industry, electrical industry, agriculture or the packaging industry, predominantly comprises thermoplastics based on polyolefins, styrene polymers, polyvinyl chloride or polyethylene terephthalate.
These used plastics, which are, in addition, valuable raw materials, can be obtained either as a mixture or as a single material. Single-material plastic waste can be produced directly in the production of plastic parts or obtained by specific collections, if necessary after separation and purification.
Hitherto, plastic recyclates have predominantly only been used for purposes where relatively low strict demands are made, for example as fillers or where thick-walled parts are used, for example noise protection dams. However, the use of recyclates in demanding applications is now increasingly intended, in particular single-material recyclates being included in these considerations.
For the stabilization of recycled high-density polyethylene, P. Vink, R. T. Rotteveel and J. D. M. Wisse in Polymer Degr. and Stability, Issue 9, p. 133 (1984) studied various stabilizers from the classes of the phosphites, hindered phenols, benzotriazoles, hindered amines and phosphonites.
These authors also indicated that the recyclates must be re-stabilized. Although the plastics have mostly originally been treated with stabilizers against thermooxidative and in some cases also against photooxidative degradation, these stabilizers are lost during use of the plastics, during storage of the waste and during processing of the recyclates, in some cases due to migration, extraction or by degradation. A recycled plastic differs structurally and also chemically from a new plastic as a consequence of the prior use or due to storage and processing; for example sites of attack for oxidative degradation may already have formed. A recycled plastic therefore requires, generally, a relatively large amount of stabilizers or alternatively stabilizers which take into account these particular circumstances. The difficulty of finding suitable stabilizers is due in particular to the type of previous damage, which may have taken place over an extended period.
From U.S. Pat. No. 4,443,572, JP-A-57/202,346, JP-A-01/020,249 and FR-A-2 528 056 it is known to use a mixture including a phenol, a pentaerythritol and a selected inorganic compound in certain virgin plastics.
Single-material recycled plastics can be obtained as production waste, for example film edge trim, sprue parts of plastic articles, pre- or post-production parts or reject parts, or in the case of separately disposed or sorted used materials, for example used automobile parts, such as battery casings or bumpers, or packaging materials, for example polystyrene foams.
It has now been found that single-material recycled plastics can be stabilized in a simple and economical manner against thermooxidative degradation by means of a mixture of stabilizers known per se, and can thus be converted in a variety of ways not only into serviceable products, but in particular into high-quality products.
Single-material plastics are taken to mean materials which comprise more than 98% of only one polymer or copolymer (for example ABS).
The invention relates to a process for the stabilization of single-material recycled thermoplastics, which can be obtained from commercial and industrial waste, which comprises adding from 0.01 to 15% by weight of a mixture of a) at least one sterically hindered phenol, b) at least one organic phosphite or phosphonate and c) at least one inorganic compound from the series consisting of metal oxides, hydroxides and carbonates.
The a:b weight ratio is preferably from 20:1 to 1:20, particularly preferably from 10:1 to 1:10, very particularly preferably from 4:1 to 1:4. The (a+b):c weight ratio is preferably from 10:1 to 1:20, particularly preferably from 5:1 to 1:10, very particularly preferably from 3:1 to 1:3.
The plastics to be stabilized are, for example, film waste, automobile battery casings, bottle crates or polystyrene foam.
The invention relates especially to the stabilization of single-material recycled plastics either from the polyolefins or from the polystyrenes.
In particular, the invention relates to the stabilization of single-material recycled plastics which comprise a polyolefin of which polyethylene, polypropylene and polypropylene copolymers are particularly preferred.
The polyolefins include, in particular, polyethylene (PE) and polypropylene (PP), in particular low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), high-density polyethylene (HDPE), ultra-low-density polyethylene (ULDPE) and medium density polyethylene (MDPE), and furthermore copolymers such as ethylene-propylene (EPM) and ethylene-propylene-diene (EPDM) copolymers.
Polystyrene (PS) is also taken to mean copolymers containing styrene, for example acrylonitrile-butadiene-styrene polymers (ABS).
Single-material recyclates may also contain, in small amounts, residues of other plastics or alternatively non-thermoplastics or foreign substances, for example paper, pigments and adhesives, which are frequently difficult to remove. These foreign substances may also originate from contact with diverse substances during use or processing, for example fuel residues, paint components, traces of metal, initiator residues or traces of water.
From 0.05 to 5% by weight of the mixture of a, b and c is preferably employed. From 0.1 to 2% by weight of the mixture of a, b and c is particularly preferably employed. From 0.1 to 1% by weight is very particularly preferably employed.
The sterically hindered phenols used as component a are known stabilizers against thermooxidative ageing of plastics, in particular polyolefins. These compounds preferably contain at least one group of the formula I
in which R′ is hydrogen, methyl or tert-butyl and
R″ is substituted or unsubstituted alkyl or substituted or unsubstituted thioether.
Examples of such sterically hindered phenols are:
2,6-di-tert-butyl-4-methylphenol, 2-tert-butyl-4,6-dimethylphenol, 2,6-di-tert-butyl-4-ethylphenol, 2,6-di-tert-butyl-4-n-butylphenol, 2,6-di-tert-butyl4-i-butylphenol, 2,6-dicyclopentyl-4-methylphenol, 2-(&agr;-methylcyclohexyl)-4,6dimethylphenol, 2,6-dioctadecyl-4-methylphenol, 2,4,6-tricyclohexylphenol, 2,6-di-tert-butyl4-methoxymethylphenol, 2,6-dinonyl-4-methylphenol, 2,6-di-tert-butyl-4-methoxyphenol, 2,5-di-tert-butylhydroquinone, 2,5-di-tert-amylhydroquinone, 2,6-diphenyl4-octa-decyloxyphenol, 2,2′-thiobis(6-tert-butyl-4-methylphenol), 2,2′-thiobis(4-octylphenol), 4,4′-thiobis(6-tert-butyl-3-methylphenol), 4,4′-thiobis(6-tert-butyl-2-methylphenol), 2,2′-methylenebis(6-tert-butyl-4-methylphenol), 2,2′-methylenebis(6-tert-butyl-4-ethylphenol), 2,2′-methylenebis[4-methyl-6-(&agr;-methylcyclohexyl)phenol], 2,2′-methylenebis(4-methyl-6-cyclohexylphenol), 2,2′-methylenebis(6-nonyl-4-methylphenol), 2,2′-methylenebis(4,6-di-tert-butylphenol), 2,2′-ethylidenebis(4,6-di-tert-butylphenol), 2,2′-ethylidenebis(6-tert-butyl-4-isobutylphenol), 2,2′-methylenebis[6-(&agr;-methylbenzyl)-4-nonylphenol], 2,2′-methylenebis[6-(&agr;,&agr;-dimethylbenzyl)-4-nonyl-pheno
Herbst Heinz
Hoffmann Kurt
Pfaendner Rudolf
Sitek Franciszek
Ciba Specialty Chemicals Corp.
Crichton David R.
Hall Luther A. R.
Reddick Judy M.
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