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
2000-04-24
2004-08-31
Acquah, Samuel A. (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...
C528S332000, C528S335000, C525S424000, C525S425000, C525S426000, C525S427000, C525S433000
Reexamination Certificate
active
06784257
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an antistatic polymer composition and more specifically to a composition comprising a thermoplastic polymer (A) and a copolymer (B) comprising polyamide blocks and polyether blocks comprising essentially ethylene oxide units —(C
2
H
4
—O)—, the copolymer (B) having a melting temperature of between 80 and 150° C. and advantageously of between 90 and 135° C.
BACKGROUND OF THE INVENTION
The invention relates to giving antistatic properties to the thermoplastic polymer (A). The formation and the retention of static electricity charges at the surface of most plastics are known. The presence of static electricity on thermoplastic films results, for example, in these films sticking to one another, making it difficult to separate them. The presence of static electricity on packaging films can result in the accumulation of dust on the items to be packaged and can thus interfere with their use. Static electricity can also damage microprocessors or components of electronic circuits. Static electricity can also bring about the combustion or the explosion of inflammable materials, such as, for example, expandable polystyrene beads, which comprise pentane.
The prior art has disclosed antistatic agents, such as ionic surfactants of the ethoxylated amine or sulphonate type, which are added to polymers.
However, the antistatic properties of the resultant polymers not only depend on the ambient humidity but are also not permanent, since such antistatic agents migrate to the surface of the polymer and disappear. Copolymers comprising polyamide blocks and polyether blocks which are hydrophilic were then provided as antistatic agents. These agents have the advantage of not migrating and therefore of giving permanent antistatic properties which are, furthermore, independent of the ambient humidity.
SUMMARY OF THE INVENTION
The aim of the present invention is to introduce permanent antistatic properties into a heat-sensitive polymer (A). It has been found to be particularly advantageous to use a copolymer (B) having a low melting temperature. The prior art has not disclosed such systems. More specically, the prior art has disclosed systems which are undesirable for the purposes of the present invention, to wit:
Patent EP 525 365 discloses antistatic compositions comprising 100 parts of PVC and 5 to 15 parts of a copolymer (i) comprising polyamide blocks and polyethylene glycol (PEG) blocks. The copolymer (i) has a melting temperature of 155.6° C., if the polyamide blocks are made of polyamide-12 (PA 12), and of 195° C., if the polyamide blocks are made of PA-6.
Patent EP 829 520 discloses antistatic compositions comprising a thermoplastic, such as PVC, polypropylene, polyethylene or ABS, and a copolymer (i) comprising polyamide blocks and polyethylene glycol blocks which is deposited on fibres. The melting temperature of (i) is not specified but the description refers to Patent EP 613 819 for the definition of (i). In the latter patent, the polyamide blocks (i) are composed of PA-6, which implies melting temperatures of at least 195° C.
Patent Application JP 05 311 022 A, published on Nov. 22, 1993 (priority 92JP-143 633), discloses mixtures of PVC, of a copolymer of an unsaturated ester and of carbon monoxide, of polyethylene glycol and of an inorganic salt chosen from alkali metal perchlorates and from alkali metal thiocyanates. The polyethylene glycol does not have a melting point but it readily migrates and therefore the antistatic properties disappear.
Accordingly preceding prior art has disclosed either polymers having an excessively high melting temperature or polymers which migrate and has therefore not disclosed the systems of the present invention.
According to a second form of the invention, the polyamide blocks of the copolymer (B) are copolyamides resulting from the condensation of at least one &agr;,&ohgr;-aminocarboxylic acid (or one lactam), at least one diamine and at least one dicarboxylic acid. An advantage of this form is that it is possible to choose comonomers of the copolyamides which improve the compatibilization of (A) and (B).
Another advantage of the compositions of the present invention relates to the polymers (A) which are not heat-sensitive but which are processed at low temperature. It is pointless to use high temperatures only to melt the copolymer (B). This is because the polyether blocks are sometimes sensitive to high temperatures and colorations of (B) are observed.
Another advantage of the compositions of the invention is their ease of preparation. This is because the compositions of the invention are generally prepared by mixing (A) and (B) in single-screw or twin-screw extruders, Busse® mixers, kneaders or any equivalent device used in thermoplastics technology. The low melting temperature facilitates the mixing of (A) and (B).
The invention will now be described in detail.
Mention may be made, as examples of polymers (A), of polyolefins, polyamides, fluorinated polymers, saturated polyesters, polycarbonate, styrene resins, PMMA, thermoplastic polyurethanes (TPU), PVC, copolymers of ethylene and of vinyl acetate (EVA), copolymers of ethylene and of an alkyl (meth)acrylate, ABS, SAN, polyacetal and polyketones. The term “polyolefins” within the meaning of the invention also denotes the copolymers of ethylene and of an &agr;-olefin. It would not be departing from the scope of the invention to use a mixture of two or more polymers (A). As regards the copolymer (B), its intrinsic viscosity in solution is advantageously between 0.8 and 1.75 dl/g. This relative viscosity is measured as a 0.5% solution in meta-cresol using an Ostwald viscometer.
The polymers comprising polyamide blocks and polyether blocks result from the copolycondensation of polyamide sequences comprising reactive ends with polyether sequences comprising reactive ends, such as, inter alia:
1) Polyamide sequences comprising diamine chain ends with polyoxyalkylene sequences comprising dicarboxyl chain ends.
2) Polyamide sequences comprising dicarboxyl chain ends with polyoxyalkylene sequences comprising diamine chain ends obtained by cyanoethylation and hydrogenation of aliphatic &agr;,&ohgr;-dihydroxylated polyoxyalkylene sequences, known as polyetherdiols.
3) Polyamide sequences comprising dicarboxyl chain ends with polyetherdiols, the products obtained being, in this specific case, polyetheresteramides. These copolymers are particularly advantageous.
The polyamide sequences comprising dicarboxyl chain ends originate, for examples, from the condensation of &agr;,&ohgr;-aminocarboxylic acids, of lactams or of dicarboxylic acids and diamines in the presence of a chain-limiting dicarboxylic acid.
According to a first form of the invention, the polyamide sequences result, for example, from the condensation of one or more &agr;,&ohgr;-aminocarboxylic acids and/or of one or more lactams having from 6 to 12 carbon atoms in the presence of a dicarboxylic acid having from 4 to 12 carbon atoms and are low in mass, that is to say {overscore (M)}n of 400 to 1000 and advantageously of 400 to 800. Mention may be made, as example of &agr;,&ohgr;-aminocarboxylic acid, of aminoundecanoic acid and aminododecanoic acid. Mention may be made, as example of dicarboxylic acid, of adipic acid, sebacic acid, isophthalic acid, butanedioic acid, 1,4-cyclohexanedicarboxylic acid, terephthalic acid, the sodium or lithium salt of sulphoisophthalic acid, dimerized fatty acids (these dimerized fatty acids have a dimer content of at least 98% and are preferably hydrogenated) and dodecanedioic acid HOOC—(CH
2
)
10
—COOH.
Mention may be made, as examples of lactams, of caprolactam and lauryllactam.
Caprolactam will be avoided, unless the polyamide is purified from the caprolactam monomer which remains dissolved therein.
Polyamide sequences obtained by condensation of lauryllactam in the presence of adipic acid or of dodecanedioic acid and with a mass {overscore (M)}n of 750 have a melting temperature of 127 -130° C.
According to a second form of the invention, the polyamide seq
Hilgers Hermann Josef
Lacroix Christophe
Linemann Reinhard
Acquah Samuel A.
Atofina
Millen White Zelano & Branigan P.C.
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