Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
2001-06-26
2004-06-08
Moore, Margaret G. (Department: 1712)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S331800, C525S331100, C525S330400, C525S330500, C525S332700, C525S332600, C525S345000, C525S347000
Reexamination Certificate
active
06747099
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to compositions of matter classified in the art of chemistry as bis-, tri- and higher poly-maleimides, as bis-, tri- and higher poly-citraconimides, as silicone elastomers, as p-phenylenediamine based antiozonants and as sulfur containing organic compounds which are accelerators for the sulfur curing (crosslinking) of polymers which are curable/crosslinkable by sulfur and also sulfur compounds which are polysulfide polymers. The invention also relates to compositions containing them, to processes for their use and to the products produced by such processes.
Polymers and copolymers crosslinked with free radical initiators, organic peroxides and/or azo initiators, are known to have superior properties, particularly to polymers crosslinked by sulfur cure. These properties include high heat ageing resistance, low compression set, decreased staining of metal or coated metal sheet and easy production of colored products which have color stability during crosslinking and during long periods of use. These properties make use of peroxide cure of great practical importance particularly because crosslinking is through a carbon carbon bond rather than through a sulfur containing linkage and this bonding difference is responsible for the improved heat aging and compression set. The drawback for cure of polymers with free radicals from organic peroxides and azo initiators has always been that if air is not excluded from the surface of the material during cure, a tacky surface due to cure inhibition by the molecular oxygen in the air results.
In order to avoid tacky surfaces on objects fabricated using such free radical crosslinking by organic peroxides and/or azo initiators, it has been conventional to exclude air from contact with the surface during cure to avoid the cure inhibition caused by the presence of the molecular oxygen found in atmospheric air. Measures to exclude molecular oxygen add to the cost and complexity of the cure step and sometimes it is difficult, as in the cases of cure in steam autoclaves and in the interior of hoses, to assure the complete exhaustion of air and its molecular oxygen component. In some cases the manufacturer would like to switch from sulfur to peroxide cure and use existing hot air oven curing chambers. Curing with conventional peroxide systems under these circumstances would not be viable as a tacky surface would result.
In order to simplify and reduce the cost and complexity of the cure step, various methods have been suggested for preventing surface cure inhibition by molecular oxygen during free radical crosslinking. These methods have, for various reasons, met with little or no success in actual practice. In particular, none have provided a tack free surface while providing the most desirable physical property of peroxide (azo) cure; superior compression set at 150° C. for 70 hours, compared to about 100° C., i.e. lower temperature performance for the prior art.
PRIOR ART
U.S. Pat. No. 4,983,685 discloses the use of compounds selected from the following classes: (a) imidazole compounds, (b) thiourea compounds, (c) thiazole compounds, (d) thiuram compounds, (e) dithiocarbamate compounds, (f) phenol compounds, (g) triazole compounds and (h) amine compounds which are accelerators for sulfur vulcanization in the optional presence of antioxidants, anti-ageing compounds and the like for elastomers for reducing surface tack in the peroxide cure of elastomers in the presence of molecular oxygen. Among optional ingredients which are suggested as possible ingredients for inclusion in the formulations, in this case for increased crosslinking, is N,N′-m-phenylene bismaleimide.
This is not the preferred optional coagent as a dimethacrylate compound is actually used in the examples. There is no recognition that this latter bismaleimide compound might provide an enhanced effect on the ability of certain compounds of (a) through (h) to reduce surface tack during free radical cure in the presence of molecular oxygen. The use of the various sulfur is accelerators, in particular with peroxide, does provide tack free or reduced tack surfaces for the cured polymers in this reference but the important physical properties expected from a peroxide cure are also reduced. There is no recognition in U.S. Pat. No. 4,983,685 that if the silicone elastomers, bismaleimides and biscitraconimides of the present invention are used in combination with p-phenylene diamine based antiozonants, sulfur containing sulfur vulcanization accelerators and antioxidants and/or polysulfide polymers in free radical cures of polymers, that tack free surfaces and improved physical properties will result and that of all the crosslinking aids mentioned, only these particular classes of compounds have that effect.
Japanese Published Patent Application No. Hei 9[1997]-169873 discloses that antioxidants of the benzimidazole type and of the polymeric 2,2,4-trimethyl-1,2-dihydroquinoline type used in combination with standard crosslinking aids such as methacrylate esters, triallylcyanurates and maleimides, such as this present invention's preferred component N,N′-m-phenylene bismaleimide, and standard crosslinking peroxides will result in cured peroxide crosslinkable elastomers with a tack free surface in the presence of air. The inclusion of p-phenylene diamine based antiozonants, silicone elastomers, sulfur accelerators of any type and/or polysulfide polymers is not suggested.
U.S. Pat. No. 4,334,043 teaches the use of surface treatment of curable polymer compositions with organo-metallic compounds, inorganic metallic salts, or lanthanides prior to crosslinking with organic peroxide crosslinking initiators in air to prevent surface tack after crosslinking. Other means of controlling surface tack are not mentioned except for the previously known techniques for surface tack free curing by simply excluding air contact with the rubber surface.
U.S. Pat. Nos. 4,814,384 and 4,973,627 disclose cures of rubber blends for tire treads and sidewalls using a combination of sulfur and peroxide cures. Sulfur accelerators are also employed. Coagents of any type are not mentioned, nor is cure in the presence of air discussed. The use of elemental sulfur is required in the practice of these inventions. We have found, however, that the use of elemental sulfur adversely affects the final physical properties of the cured elastomer to the point where they are more typical of sulfur cure than peroxide cure.
U.S. Pat. No. 4,743,656 also discloses a mixed sulfur/peroxide cure agent for elastomers, which cure agent also includes sulfur accelerators as well as elemental sulfur and the peroxide. Coagents are not mentioned, nor are crosslinking in air and surface tackiness discussed.
U.S. Pat. No. 4,575,552 claims the use of specific combinations of hindered phenol antioxidants, metal salts of dithiocarbamates and m-phenylene-dimaleimide to provide a peroxide crosslinked polymer with superior hydrolytic and thermal stability for geothermal applications. There is no mention of crosslinking in the presence of air, air-inhibition or surface tackiness as a result of air-inhibition.
U.S. Pat. No. 5,849,214 discloses the use of sulfur compounds, sulfur accelerators and hydroquinones with the optional presence of crosslinking aids (coagents) in the retardation of scorch during compounding of free radical crosslinkable polymers in the presence of free radical initiators. Bismaleimides, and biscitraconimides are not specifically discussed nor is there any mention of the possible effect on surface tackiness during cure in the presence of molecular oxygen (air) for any of the compositions disclosed.
In addition there are patents which use various compounds to physically coat the surface of crosslinkable elastomers to exclude air (oxygen) e.g., U.S. Pat. No. 4,439,388 which teaches use of boric acid, boric acid anhydride as a surface treatment prior hot air cure. This surface coating technique is labor intensive as it must be removed and disposed of after the cro
Gullo Gary J.
Novits Michael F.
Palys Leonard H.
ATOFINA Chemicals, Inc.
Mitchell William D.
Moore Margaret G.
LandOfFree
Tack free surface cures of polymers by organic peroxides in... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Tack free surface cures of polymers by organic peroxides in..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Tack free surface cures of polymers by organic peroxides in... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3353163