Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Reexamination Certificate
2000-01-28
2003-08-26
Mulcahy, Peter D. (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
C524S388000, C568S558000
Reexamination Certificate
active
06610768
ABSTRACT:
The present invention relates to cross-linking compositions. More particularly, it relates to cross-linking compositions used for cross-linking thermoplastic resins and elastomers such as rubbers.
Thermoplastic resins such as copolymers of ethylene and ethylene vinyl acetate and elastomers such as ethylene propylene diene rubber and butadiene acrylonitrile copolymer are of high economic value because they generally are available at low cost and have acceptable physical and other properties. It is known to adapt some properties, like improvement of the heat resistance, to specific needs by cross-linking these thermoplastic resins and elastomers. Typically, this is achieved by contacting the resin and/or elastomer with a proper amount of an organic peroxide and heat-treating the mixture. This, rather simple, cross-linking process has been used extensively on an industrial scale.
However, numerous problems were encountered when organic peroxides as such were used in cross-linking processes of resins/elastomers. A major problem was found to be the proper distribution of the peroxide in the resin/elastomer prior to and during the cross-linking process. More specifically, proper homogenization of the peroxide and the elastomer, optionally together with other ingredients that are part of the elastomer formulation, requires thorough mixing at a temperature allowing mastication/mixing of the elastomer. This thorough mixing generally is not feasible. First of all, economic considerations stand in the way of a lengthy mixing process. Secondly, a reduction of the mixing time, e.g., by using more mixing energy or increasing the mixing temperature, generally is not possible because of the thermal instability of the organic peroxide. More particularly, when mixing the granulate and the elastomer in conventional mixing equipment, such as mixers, kneaders, and extruders, the already elevated temperature of the elastomer increases due to the mixing energy. A too high mixing energy leads to an unacceptable temperature increase, resulting in premature decomposition of the peroxide, which is undesired from both a quality and a safety point of view.
To reduce this problem, the skilled person generally makes use of a powdery formulation of an organic peroxide on an inactive filler carrier (i.e. a filler that is inert during the processing of an elastomer, such as calcium carbonate, silica, clay, etc.). Alternatively, use is made of sheet-like or granular masterbatches, i.e. formulations of one or more peroxides and one or more resins and/or rubbers the peroxide concentration of which is greater than is desired in the cross-linking process. Such a masterbatch is detailed in, for instance, JP-07165990-A, where 10-50% of a peroxide is dispersed in a H-NBR.
However, such formulations still suffer from various drawbacks. To further improve masterbatches, JP-06049225-A proposes to also incorporate 2,4-diphenyl-4-methyl-1-pentene. In the international patent application published as WO94/29372 it is proposed to make compositions of peroxides, EP(D)M, and a polyoctenamer compound. European Patent application 227 048 discloses the use of blends of two polymers having different melt temperatures as the carrier for peroxide compounds such as dicumyl peroxide.
Furthermore, if a conventional powdery masterbatch is used, such a masterbatch will lower the kneadability (increase the viscosity) of the elastomer due to the presence of the inactive filter. Therefore, the improved dispersibility during initial mixing with the resin/rubber typically is offset by increased kneading times due to the decreased kneadability. Also, dust is easily liberated during the kneading, which may adversely affect the working environment.
The alternative sheet-like or granular masterbatches, as obtained for example by kneading and impregnating EPM or EPDM with a Mooney viscosity of about 20 to 150 (ML1+4 at 100° C.) with a peroxide, typically suffer from increasing hardness over time. Accordingly, when stored for a prolonged time, it is more and more difficult to disperse them in the elastomer to be cross-linked and a homogeneous (uniform) cross-linked resin/rubber product is difficult to obtain. Also, it is often observed that organic peroxides which are solid at 25° C. migrate to the surface of such a masterbatch, which process is known as blooming. Such blooming, leading to the formation of solid pure peroxide on the surface of said masterbatch, can result in the collection of pure peroxide in the package, which is undesired from a safety as well as a quality point of view. In the case of masterbatches of organic peroxide which are liquid at 25° C. it is known that the peroxide migrates to the surface of the masterbatch during storage, which is known as bleeding. As discussed for blooming, bleeding likewise leads to contamination of the containers and the handling equipment with pure peroxide, which is undesired from a safety point of view. Also, it is unlikely that the liquid organic peroxide will be homogeneously distributed throughout the masterbatch in a container. This is undesired since in that case quality control of the cross-linking process will become problematic. Hereinafter the term exudation is used for both the bleeding and the blooming phenomenon.
Furthermore, sheet-like or granular cross-linking agent masterbatches according to the prior art were found to be limited, in practice, to products with a maximum organic peroxide content of about 40 wt. %, while higher concentrations are desired from an economic point of view.
Moreover, conventional peroxide formulations typically suffer from 1) the necessity to use expensive processes to make such masterbatches, since they often contain a poorly processable elastomeric carrier, 2) the use of relatively expensive further additives, and/or 3) the presence of a particular elastomer/polymer in the masterbatch which limits its use to cross-linking processes where this elastomer is acceptable.
Hence there is a need for peroxide compositions not suffering from these disadvantages.
We have now found that, surprisingly, cross-linking organic peroxide compositions can be produced which are easily blended into elastomers, are widely acceptable in elastomer formulations, comprise relatively inexpensive compounds, and are easily produced at lower temperatures. Preferred compositions are “soft granular” as explained below. When the compositions according to the invention, and in particular the preferred soft granulates, are compared with masterbatch compositions according to the prior art, they show comparable mixing behaviour when blended with an elastomer, reduced exudation, and, if so desired, a high organic peroxide content. Compared with formulations consisting essentially of peroxide and filler, they show exceptionally good mixing behaviour and reduced exudation and, for formulations of solid peroxides, friability. They were found to be very suitable for use in cross-linking processes of resins and elastomers, particularly those involving cross-linking of EPM and/or EPDM.
The compositions according to the convention comprise a particular carrier material, which hereinafter is called a softening agent, having a Brookfield viscosity of 10,000 poises or less at 60° C. Preferably, the Brookfield viscosity of said softening agent is at least 5, preferably at least 500, and more preferably more than 5000 mPa·s at 20° C., for improved blendability with the rubber to be cross-linked. Depending on the peroxide to be comprised and the presence of optional further materials, preferred softening agents are alkylbenzenes, EP(D)M, and other low molecular weight polymers with said viscosity, hereinafter called liquid low molecular weight polymers, such as liquid EPM, liquid EPDM, and liquid isobutylene. Most preferred softening agents are free of aromatics and, more preferably, selected from liquid low molecular weight polymers.
It is noted that DE 196 19 509 discloses the use of liquid EPM in formulations for rubber chemicals in general. However, in these formulations a large quantity of
Drost Gerrit Frits
Ishiwatari Akio
Jelenic Jernej
Tkai Akihiko
Van Moorsel Frans Johannes
Akzo Nobel N. V.
Fennelly Richard P.
Mulcahy Peter D.
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