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
2000-12-01
2003-02-25
Seidleck, James J. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S181000, C525S184000, C525S066000, C198S643000, C198S957000
Reexamination Certificate
active
06525137
ABSTRACT:
The present invention relates to polyamide conveyor elements and more particularly (i) to fixed profiles such as slideways and rails and (ii) to moving parts such as chain links which form all or part of the moving elements of the conveyor.
The present invention is particularly useful for chain conveyors. For example, Links from 1 to 5 cm in length, from 1 to 2 cm in width and from 1 to 2 cm in thickness are assembled in order to form an endless conveyor belt. It is possible, for example, to arrange from 1 to 10 links in the width direction, in order to form a belt from 1 to 20 cm in width, and several hundreds of links in the longitudinal direction along the length of the endless belt. The links are joined together but are articulated—thus they have a relative mobility so that the conveyor belt that they form can rotate, rise or fall. The fixed part consists of rails, slideways or plates over which the links of the chain slide.
A drive system, consisting of a roller or a toothed wheel and driven by a motor, moves the conveyor belt formed by all the links forwards. The links located on the outside of the belt may be provided with hooks or have a different shape from the other links because they are often used for guiding the belt and these links slide over fixed parts of the conveyor. Those links located on the inside of the belt may slide over a plate or over profiles. Usually, the links are obtained by moulding polymers and the fixed parts of the conveyor are made of stainless steel.
The links wear away by friction with the stainless steel. Fixed metal parts of the conveyor may be covered with a polyethylene wearing piece. In general, the links are made of polyacetal (polyoxymethylene). Polyacetals are described in Ullmann's Encyclopaedia of Industrial Chemistry, 5th Edition (1992), vol. A 21, pp 591-603.
Examples of chain conveyors are described in U.S. Pat. Nos. 5,749,454, 5,031,757, 5,497,874, 5,584,373 and 5,690,210.
The prior art, in U.S. Pat. No. 5,683,818, has described blends of nylon-6,6 and polypropylene which have to withstand friction on an unlubricated metal surface. These blends also comprise a maleicized polypropylene as compatibilizer and, optionally, polytetrafluoroethylene powder as lubricant. U.S. Pat. No. 5,504,139 describes blends of PA-6,6, high-density polyethylene and a maleicized ethylene-propylene as compatibilizer. These blends are presented as having to withstand friction.
JP 63,314,256 A describes blends of a polyamide and a copolymer of ethylene, an unsaturated carboxylic acid ester and maleic anhydride. It is stated that these blends withstand friction.
EP 234,819 describes blends similar to the above prior art and they are presented as being abrasion resistant.
EP 284,379 describes blends consisting of a polyamide matrix in which nodules of an ethylene-alkyl (meth)acrylate-maleic anhydride copolymer are dispersed, and dispersed in these nodules are polyamide nodules. These blends are also presented as having to be abrasion resistant.
U.S. Pat. No. 4,391,951 describes blends of nylon-6 (at least 50%), polytetrafluoroethylene (PTFE), polyethylene having a very high molar mass and an elastomeric polyester. This composition is supposed to extend the lifetime of the nylon-6 when it is subjected to friction.
The withstand behaviour of all these products is, to a greater or lesser extent, good.
The Applicant has found that conveyor elements made of particular blends of polyamide and polyolefin exhibited exceptional wear resistance when they slid over fixed elements made of polyacetal, and vice versa.
The present invention relates to an improvement to conveyors in which at least one moving element made of a polyamide-based blend (A) slides over a fixed element made of polyacetal and/or in which at least one moving element made of polyacetal slides over a fixed element made of a polyamide-based blend (A).
With regard to the blend (A), this has a polyamide matrix and contains polyolefin nodules.
The term “polyamide” should be understood to mean the products from condensation:
of one or more amino acids, such as aminocaproic, 7-aminoheptanoic, 11-aminoundecanoic and 12-aminododecanoic acids and of one or more lactams, such as caprolactam, oenantholactam and lauryl lactam;
of one or more salts or mixtures of diamines, such as hexamethylenediamine, dodecamethylenediamine, metaxylylenediamine, bis-p-aminocyclohexylmethane and trimethylhexamethylenediamine with diacids, such as isophthalic, terephthalic, adipic, azelaic, suberic, sebacic and dodecanedicarboxylic acids;
or mixtures of certain monomers, resulting in copolyamides.
It is possible to use polyamide blends. Advantageously, PA-6 and PA-6,6 are used.
The term “polyolefins” should be understood to mean polymers comprising olefin repeat units, such as, for example, ethylene repeat units, propylene repeat units, 1-butene repeat units, etc.
By way of example, mention may be made of:
polyethylene, polypropylene and copolymers of ethylene with alpha-olefins. These products may be grafted by anhydrides of unsaturated carboxylic acids, such as maleic anhydride, or unsaturated epoxides, such as glycidyl methacrylate;
ethylene copolymers with at least one product chosen from (i) unsaturated carboxylic acids, their salts or their esters, (ii) vinyl esters of saturated carboxylic acids, (iii) unsaturated dicarboxylic acids, their salts, their esters, their semi-esters or their anhydrides, and (iv) unsaturated epoxides. These ethylene copolymers may be grafted by anhydrides of unsaturated dicarboxylic acids or by unsaturated epoxides;
styrene/ethylene-butene/styrene block copolymers (SEBS), these optionally being maleicized.
It is possible to use blends of two or more of these polyolefins.
It is advantageous to use:
polyethylene,
ethylene/alpha-olefin copolymers,
ethylene/alkyl (meth)acrylate copolymers,
ethylene/alkyl (meth)acrylate/maleic anhydride copolymers, the maleic anydride being grafted or copolymerized,
ethylene/alkyl (meth)acrylate/glycidyl methacrylate copolymers, the glycidyl methacrylate being grafted or copolymerized,
polypropylene.
In order to make it easier to form the polyamide matrix and if the polyolefins have few or no functional groups which can facilitate compatibilization, it is recommended to add a compatibilizer.
The compatibilizer is a product known per se for compatibilizing polyamides and polyolefins.
For example, mention may be made of:
polyethylene, polypropylene, ethylene/propylene copolymers and ethylene/butene copolymers, all these products being grafted by maleic anhydride or glycidyl methacrylate;
ethylene/alkyl (meth)acrylate/maleic anhydride copolymers, the maleic anhydride being grafted or copolymerized;
ethylene/vinyl acetate/maleic anhydride copolymers, the maleic anhydride being grafted or copolymerized;
the above two copolymers in which the maleic anhydride is replaced by glycidyl methacrylate;
ethylene/(meth)acrylic acid copolymers and optionally their salts;
polyethylene, polypropylene or ethylenepropylene copolymers, these polymers being grafted by a product having a site which reacts with amines, these grafted copolymers then being condensed with polyamides or oligomers of polyamides having only a single amine end group.
These products are described in EP 342,066, the contents of which are incorporated in the present application.
The amount of polyamide forming the matrix may be between 55 and 95 parts per 5 to 45 parts of polyolefins.
The amount of compatibilizer is the amount sufficient for the polyolefin to be dispersed in the form of nodules in the polyamide matrix. It may represent up to 20% of the weight of the polyolefin. These polymers are manufactured by blending a polyamide, a polyolefin and optionally a compatibilizer using the standard techniques of melt blending (twin-screw, Buss and single-screw melt blending).
Advantageously, the MFI of the polyamide is between 2 and 30 (2.16 kg/235° C.).
Advantageously, the viscosity of the dispersed phase (the polyolefin) is greater than that of the matrix.
Advantageously, the ratio of the viscosity of the poly
Alex Patrick
Knudsen Christian Capion
Rosenkrands Niels Peter
Atofina
Bissett Melanie
Millen White Zelano & Branigan P.C.
Seidleck James J.
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