Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Treating polymer containing material or treating a solid...
Reexamination Certificate
1999-09-01
2001-04-17
Truong, Duc (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Treating polymer containing material or treating a solid...
C528S500000, C528S503000
Reexamination Certificate
active
06218504
ABSTRACT:
The invention relates to a process to deodorize polyolefins, and also to the use of deodorized polyolefin granules to produce polyolefin-containing plastic moldings with low taste-impairment and odor-impairment.
Plastic moldings produced from polyolefins are of great industrial importance; since polyolefins, as saturated hydrocarbons, are to a large extent chemically inert such moldings have, inter alia, a wide variety of applications in the production of domestic products and domestic electrical devices, as packaging materials, eg. for foods, and also as piping, eg. for cold-water and hot-water supply lines.
In the preparation and processing of raw materials for plastics, on the one hand additives, such as stabilizers, plasticizers, etc. are added to the polyolefins, and on the other hand low concentrations of monomeric building blocks remain behind. Although the raw materials and additives used, and also the concentration of residual chemical building blocks in the plastic moldings produced from these materials, are not hazardous under food legislation and in terms of industrial hygiene, in some applications the odor and taste perceived by the individual are impaired.
For this reason, deodorants, ie. agents to improve odor, which merely conceal the undesirable odor and taste properties, are used to deodorize products from the domestic goods, plastics, coatings and colorants, textile and detergent industries.
There is also a known process for reducing chlorine contents and residual solvent contents during production of polypropylene powders (DE-A-3025051). Granules are produced from powders treated in this way, with addition of stabilizers. Plastic moldings which are produced from this material, however, exhibit noticeable odor-impairment and taste-impairment.
It is an object of the present invention to provide a process which, in a satisfactory manner, can improve the characteristic odor and taste which are typical of polyolefin moldings.
We have found that this object is achieved by means of a process to deodorize polyolefin granules, which comprises passing a gaseous mixture of steam and air, a gaseous mixture of steam and nitrogen (N
2
), or pure steam, around the polyolefin granules.
Surprisingly, it has been found that polyolefin granules around which a steam/air mixture, a steam
itrogen mixture, or pure steam, has been passed have markedly improved oder and taste properties, which are reproduced in the plastic moldings produced therefrom, for example by extrusion or injection molding.
The novel process may be operated continuously or discontinuously, at atmospheric pressure, at elevated pressure, advantageously up to 10 bar, or at reduced pressure. The amounts of steam used per unit are from 0.01 to 2 kg of steam per kg of polyolefin granules, advantageously from 0.3 to 2 kg of steam per kg of polyolefin granules. The temperature is generally from 80 to 150° C., preferably from 90 to 130° C. The granules may be introduced into the apparatus in wet or dry, and cold or heated, form. Depending on how the process is executed, the duration of treatment may be a few minutes or several hours. With elevated pressure, a high amount of steam per unit and high temperature, the duration of treatment may, for example, be from only 2 to 30 minutes; with other methods it may be up to 48 hours. A duration of treatment of from 1 to 10 hours is advantageous and of industrial interest.
In addition, the invention provides the use of the polyolefin granules treated by the novel process as a material for coating or producing shaped objects, in particular for application as domestic goods and as piping.
The polyolefin granules used according to the invention include granules which comprise polyolefins of the structure
where each of R
1
and R
2
is hydrogen, a straight-chain or branched saturated aliphatic radical having from 1 to 6 carbon atoms or a cycloaliphatic group. Granules which comprise polyolefin copolymers are also included.
Preferred polyolefins are polyethylenes (PE), polypropylenes (PP), poly-1-butenes (PB), polyisobutenes and poly-4-methyl-1-pentenes, and also copolymers of ethylene and propylene (ie. random copolymers and polyolefin rubbers), terpolymers of ethylene, propylene and hydrocarbons which contain two or more non-conjugated double bonds (ie. polyolefin elastomers) and mixtures of PP, rubber and PE, which are prepared, for example, by coextrusion (extruder blends) or in situ (C2/C3 reactor blends).
The novel process may be used with particular advantage on pipe materials made from polyethylene or polypropylene, in particular on PP materials which have an MFI (230/5) of from 0.4 to 2 dg/min and an ethylene content of from 0.0 to 11% by weight and are in the form of granules. These materials are supplied by various polyolefin producers and may be pigmented or unpigmented.
Depending on the application, the polyolefin granules used according to the invention may also contain additives, for example stabilizers, plasticizers, colorants, agents to protect against the action of light, flame retardants, antioxidants or nucleating agents, and/or fillers, for example chalk, talc, mica, glass fiber or glass beads.
Possible apparatus for carrying out the deodorization of the polyolefin granules are extraction columns, flow tubes, filter screens, mixing vessels, pressure vessels, silos and fluidized-bed reactors, but preferably mixing vessels, pressure vessels or silos. All of the apparatus which can be used according to the invention share the feature that the polyolefin granules are subjected to a steam treatment, in particular to a steam distillation or steam extraction in the apparatus. Air or nitrogen may be added to the steam here. Possible versions of the novel process are described in the examples. A characteristic feature of the deodorization process is the treatment of granules. However, the process can also be used to deodorize plastic moldings.
To judge the odor-impairment or taste-impairment by each type of polyolefin granule, the threshold value for odor or taste (TVOT) is determined in an oder or taste test. The detailed specification is laid out in Example 2.
The deodorized polyolefin granules may be used to produce hollow bodies, piping, packaging materials, packaging films, filters, hygiene fabrics, casings for white goods (e.g. coffee machines) and polyolefin sheets for the construction of equipment. The deodorized polyolefin granules are particularly suitable for producing supply lines for cold and hot water for drinking, water tanks, drinking cups and food packaging.
The polyolefin molding compositions may be brought into their desired final form by usual processes, such as compression molding, casting, calendering, extruding, blow molding, injection molding, etc.
REFERENCES:
patent: 4332933 (1982-06-01), Di Drusco et al.
patent: 4666994 (1987-05-01), Zboril
patent: 5191062 (1993-03-01), Bernier et al.
patent: 2175158 (1996-10-01), None
patent: 2198177 (1997-08-01), None
patent: 4 601 (1979-10-01), None
patent: 96/11216 (1996-04-01), None
Carrion Eduardo Chicote
Dolle Volker
Schöneborn Paul-Richard
Terwyen Herbert
Keil & Weinkauf
Targor GmbH
Truong Duc
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