Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Compositions to be polymerized by wave energy wherein said...
Reexamination Certificate
1999-07-22
2002-06-04
Berman, Susan W. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Compositions to be polymerized by wave energy wherein said...
C522S153000, C522S154000, C522S157000, C522S158000, C522S159000, C522S160000, C522S161000, C522S112000, C522S071000, C526S328000, C526S335000, C526S340000, C526S341000, C526S348600, C526S348800
Reexamination Certificate
active
06399671
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to rubber polymers based on polymerizable monomers and having an elevated gel content together with an elevated degree of swelling, to the production of the stated rubber polymers and to the use thereof for the production of moldings of all kinds.
BACKGROUND OF THE INVENTION
The low viscosity of many rubber polymers obtainable according to the prior art, in particular of ethylene/vinyl acetate rubbers or ethylene/acrylate rubbers or acrylate rubbers, gives rise to considerable problems during processing which makes it impossible to use them in many industrial applications. Such problems are, for example, sticking on rollers, inadequate rigidity during profile production or insufficient melt pressure during injection molding.
In the prior art, care has hitherto also been taken during the production of rubber polymers to ensure that the gel content of the resultant rubber polymers was as low as possible in order, by and large, to permit direct processability of the resultant rubber polymers. The gel content of the rubber polymers in such cases was conventionally up to approx. 20 wt. %. The gel content of the polymers was established in such cases in the conventional manner by chemical and/or physical crosslinking, for example by radiation crosslinking or by crosslinking with sulfur or compounds containing sulfur and peroxide compounds.
W. Hofmann accordingly provides a comprehensive description of the radiation crosslinking of elastomers in
Rubber Technology Handbook
, page 403 to 406, Hanser Publishers, Munich, Vienna, New York, 1989. Crosslinking with high energy&ggr; radiation is moreover described in
Handbuch für Vulkanisation und Vulkanisationshilfsmitteln
, published by Bayer AG, Leverkusen, 1965, pages 359-363. Unfortunately, polymers treated according to the prior art may frequently be processed in conventional processing apparatus only with difficulty.
SUMMARY OF THE INVENTION
The object of the present invention was to provide rubber polymers which may straightforwardly be processed in conventional rubber processing machinery. This means that no sticking to the roller occurs during production and further processing of rubber compositions, adequate rigidity after shaping is ensured and furthermore the formation of bubbles is, for example, prevented in injection molding.
The present invention provides rubber polymers based on polymerizable monomers and having a gel content of 40 to 80%, relative to the entire quantity of polymer, and a swelling index of 30 to 75, relative to the gel, wherein the gel content and swelling index are established by treatment with &ggr; radiation.
Furthermore, the present invention provides the use of the rubber polymers produced according to the present invention for the production of moldings or films of all kinds.
DETAILED DESCRIPTION OF THE INVENTION
The gel content and swelling index of the rubber polymers according to the present invention are determined using the following method:
The sample is placed in methylene chloride, to which 1 g/l of lonol had been added, such that there were 12.5 g of polymer per liter of solvent. The mixture is shaken for 6 hours at 140° C., then centrifuged for 1 hour at 20,000 rpm, wherein the temperature was still maintained at 140° C. The sol solution was separated and may optionally be further investigated. The gel is first weighed while moist and the quantity of the dry gel obtained after drying to constant weight in a vacuum drying cabinet is determined.
The percentage gel content and the swelling index are calculated using the following formulae:
Gel
content
=
mass
of
dry
gel
total
initial
weight
of
sample
·
100
Swelling
index
=
mass
of
moist
gel
mass
of
dry
gel
The rubber polymers according to the present invention preferably have a gel content of 30 to 80%, particularly preferably of 40 to 70%. The swelling index is preferably 30 to 75, particularly preferably 40 to 60.
The rubber polymers according to the present invention are synthesized from polymerizable monomers which may be used individually or in any desired mixtures with each other. The particular favorable mixture ratio is determined by the intended purpose of the moldings to be produced from the rubber polymers and may readily be determined by appropriate preliminary testing.
Polymerizable monomers which may be considered are ethylenically unsaturated monomers, dienes or trienes. The monomers may optionally be substituted, wherein the substituents may be selected from among halogen, in particular chlorine, bromine and iodine, optionally substituted alkyl groups, in particular methyl, ethyl, n-propyl, iso-propyl, n-butyl, sec.-butyl, iso-butyl, tert.-butyl, n-pentyl, n-hexyl, optionally substituted alkoxy groups, in particular methoxy, ethoxy, n-propoxy, iso-propoxy, n-butoxy, sec.-butoxy, tert.-butoxy, iso-butoxy, optionally substituted aryl groups, in particular phenyl, tolyl, optionally substituted aryloxy groups, in particular phenoxy, p-methylphenoxy, optionally substituted oxycarbonyl groups, in particular acetoxy, propionyloxy, butyryloxy, optionally substituted carboxyl groups or esterified carboxyl groups, in particular methyl carboxylate, ethyl carboxylate, propyl carboxylate, optionally substituted cyano, sulfonate, vinyl ester, vinyl-ether and allyl groups. In the event that the substituents are further substituted, these substituents are preferably substituted with C
1
-C
20
groups or halogens.
Particularly preferred monomers are ethylene, propylene, 1-butene, 2-butene, 1-pentene, chloroethylene, styrene, methyl acrylate, methyl methacrylate, ethyl methacrylate, methacrylic acid, vinyl acetate, maleic acid mono- and diester methyl vinyl ether, ethyl vinyl ether, cyanoacrylate, butadiene, isoprene, chloroprene and ethylidenenorbornene.
Very particularly preferred rubber polymers are those synthesized from ethylene and vinyl acetate, from ethylene and the above-stated acrylates and from the pure above-stated acrylates.
In the above-stated polymers, the mixture ratio of the monomers relative to each other is conventionally 0.1%-99.9%, in particular 5%-95%, very particularly preferably 30%-80%.
The gel content and degree of swelling of the rubber polymers according to the invention is established by ionizing radiation. Treatment with &ggr; radiation is preferably considered as the ionizing radiation.
In order to be able to establish the gel content and degree of swelling of the rubber polymers according to the invention, the treatment with ionizing &ggr; radiation is performed at a radiation dose of 20 to 140, preferably of 60 to 120, in particular of 70 to 100 kGy (kilogray). Irradiation may be performed using any desired plant suitable for this purpose, for example with a 3.5 MCi
60
Co gamma plant (approx. 1.3 MeV). Apart from Co-60 radiation, radiation from the
137
Cs isotope is also suitable. The applied radiation dose may, for example, be measured using a photometric system from Far West Technology, USA and the film dosimeter supplied by this company. These film dosimeters contain a radiation-sensitive dye and the radiation dose is calculated on completion of the irradiation process from the change in the absorbance of said dye.
These dosimeters are calibrated ex works against an internationally recognized standard.
Treatment with &ggr; radiation may be performed in the conventional manner at temperatures of 0° to 130°, preferably of 10° to 120°, in particular of 20 to 80° C. The most favorable temperature range may readily be determined by appropriate preliminary testing. It is essential that the temperature range is selected such that adequate free radical mobility is ensured.
The rubber polymers according to the present invention are preferably produced by initially polymerizing the monomers used in a conventiona
Hoch Martin
Meisenheimer Hermann
Sesterhenn Lothar
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