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
1999-04-06
2001-05-15
Niland, Patrick D. (Department: 1714)
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...
C523S351000, C524S495000, C524S496000, C525S330400
Reexamination Certificate
active
06232394
ABSTRACT:
The present invention relates to master batches containing vulcanization agents and more particularly thermoplastic master batches having copolymers of ethylene and of at least one unsaturated carboxylic acid ester as support. They are useful, for example, for introducing vulcanization agents into elastomers. The invention also relates to a process for the preparation of master batches containing vulcanization agents and having thermoplastic ethylene copolymers as support.
Vulcanized elastomers result from the mixing of an elastomer such as, for example, a styrene/butadiene copolymer with fillers, plasticizers, antioxidants, a vulcanization agent, one or more accelerators and optionally an activator, after which this mixture is shaped and heated in order to bring about the vulcanization, which is a crosslinking reaction.
The vulcanization agents, accelerator, activator and antioxidants are used at relatively low doses when compared with the other ingredients (fillers, plasticizers). Since they play a fundamental role in the crosslinking reaction, it is necessary for them to be optimally distributed in the mixture to be vulcanized. For this, these products are advantageously introduced into the mixture in the form of master batches.
As a general rule, these master batches use an elastomer as support, such as an EPDM (ethylene/propylene/diene copolymer), an EPR (ethylene/propylene copolymer), an SBR (styrene/butadiene copolymer) or an NBR (nitrile/butadiene copolymer).
By definition, these master batches contain a large amount of additives. It is necessary to choose as support a polymer which can be readily dispersed in the mixture to be vulcanized.
It is thus advantageous for this support to have an affinity with the mixtures to be vulcanized.
These master batches are generally in the form of strips or granules. One of the difficulties encountered in their use lies in their tendency to agglomerate during storage. This phenomenon is due to the tacky nature of the support at the usual storage temperatures. This agglomeration often prevents the product from being used in the usual transportation and automatic weighing installations with which mixing plants are equipped.
According to the prior art, this drawback is overcome by adding an anti-tack agent, for example talc, which is added by spraying during granulation or manufacture of the master batch strips. This process has the drawback of introducing an additional product which it is always difficult to distribute uniformly.
The Applicant has now found that master batches having copolymers of ethylene and of unsaturated carboxylic acid esters as support have many advantages.
By virtue of their polarity, these ethylene polymers disperse readily in most polymers; they have a low Vicat point, which facilitates dispersion of the master batch, and, lastly, the master batch is solid and non-tacky at room temperature, which prevents any agglomeration on storage whether the product is presented in strip form or granule form and this being with the optional addition of small amounts of anti-adhesive agent such as, for example, talc. By using the master batches of the present invention to vulcanize elastomers, no degradation of the properties of vulcanized rubbers are observed when compared with rubbers vulcanized with the master batches of the prior art.
The present invention relates to thermoplastic master batches having at least one copolymer (A) of ethylene and of at least one unsaturated carboxylic acid ester as support and comprising vulcanization agents.
By way of example, mention may be made of:
sulphur-containing vulcanization systems consisting of sulphur combined with vulcanization accelerators such as metal salts of dithiocarbamates (zinc, tellurium, etc. dimethyldithiocarbamate), thiuram mono-, di- and tetrasulphides (thiuram tetramethyl disulphide, etc.), sulpheramides, morpholine derivatives and guanidines.
These systems can also contain zinc oxide optionally combined with stearic acid, which are vulcanization activators for diene elastomers,
sulphur-donating vulcanization systems in which most of the sulphur used for the crosslinking comes from sulphur-containing molecules such as thiuram polysulphides, mercaptobenzothiazole disulphide etc.,
vulcanization systems based on metal oxides, particularly for halogen-containing elastomers (for example polychloroprene). This particularly relates to zinc oxide,
vulcanization systems containing phenolic resins consisting of difunctional phenol-formaldehyde resins which may contain halogen and be combined with metal chlorides or zinc oxide,
peroxide-containing vulcanization systems in which all free-radical donors can be used, for example dicumyl peroxide, combined with zinc oxide and stearic acid,
vulcanization agents based on diamines (ortho-toluidylguanidine, diphenylguanidine, etc.) or on blocked diamines such as hexamethylenediamine carbamate,
acceleration systems based on thiourea derivatives such as ethylthiourea or diethylthiourea.
The master batches of the invention can also contain one or more of the following products:
antioxidants,
anti-ozonizers,
ultraviolet-absorbing agents,
swelling agents,
carbon black.
The master batches might contain only some of the vulcanization system, such as the sulphur, and the accelerator could be added separately to the elastomer.
It would not be considered a departure from the scope of the invention if the master batches also contained the other usual additives in elastomers to be vulcanized, such as plasticizers, carbon black, silica, carbonate, talc or flame-retardants. These additives are often present in the same or larger amounts than the elastomer itself and are always in much larger amounts than the vulcanization system. Such a master batch would be pointless. However, the master batches of the invention can contain a small amount of plasticizer, as will be explained later.
The elastomers to be vulcanized can be, for example, natural rubber, polyisoprene, SBR, NBR, EPDM, polychloroprene, butyl rubber or polyethers such as epichlorohydrin rubbers.
As regards the copolymer (A), the esters can come from the reaction of an unsaturated carboxylic acid with a monoalcohol having from 1 to 24 carbon atoms. By way of example, mention may be made of alkyl (meth)acrylates in which the alkyl has from 1 to 24 carbon atoms. Examples of acrylates or of methacrylates are methyl methacrylate, ethyl acrylate, n-butyl acrylate, isobutyl acrylate and 2-ethylhexyl acrylate. These eaters can be introduced into A by grafting (onto polyethylenes) or by direct copolymerization.
The amount of additives (i.e. of vulcanization agents and of other optional products) can be from 50 to 90% by weight of the master batch. Advantageously, this amount is from 80 to 90%. The density of the master batches can thus be between 1.1 and 5.5.
Advantageously, the copolymer (A) is such that the master batch is solid and non-tacky at room temperature and plastic at the operating temperatures, i.e. during mixing with the polymer and the other additives added to the polymer along with the master batch. This temperature can vary with the nature of the polymer and of the additives; as a general rule, the elastomer and all its additives, including the master batch of the invention, cannot be mixed above 100 or 110° C. without running the risk of causing vulcanization to start.
The master batches of the invention are plastic, advantageously at temperatures above 80 or 90° C. They can thus be dispersed in polymers while at the same time remaining in a region in which there is no risk, for example, of prevulcanization.
By way of example, the Mooney ML 1+4 viscosity at 50° C. of the master batches is between 15 and 25.
The master batch can comprise a plasticizer such as, for example, a paraffinic or naphthenic oil in order to facilitate the incorporation of the additives and/or to adjust the viscosity.
The Applicant has found that for the master batch to keep to the above conditions, i.e. to be solid at room temperature and plastic at the operating temperatures, it is advantageous
Bonhomme Dominique
El Bounia Eddine Nour
Pfrengle Walter
Pierrot Jean-Michel
Elf Atochem S.A.
Millen White Zelano & Branigan P.C.
Niland Patrick D.
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