Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Compositions to be polymerized by wave energy wherein said...
Reexamination Certificate
1998-05-15
2002-10-01
Sergent, Rabon (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Compositions to be polymerized by wave energy wherein said...
C522S097000, C522S098000, C525S453000, C528S061000, C528S064000, C528S065000, C528S075000, C528S906000
Reexamination Certificate
active
06458866
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to polyurethane elastomers with specific structural units, a method for their production as well as their use in melt-spin and extrusion processes for the production of films or fibers.
BACKGROUND OF THE PRIOR ART
Polyurethane elastomers are block copolymers built of regularly arranged soft and hard segments. The soft segments comprise long, randomly arranged and flexible chains which lend to the fibers the requisite rubber-like elasticity. The properties can be varied with the relative molar mass and the type of soft segment with respect to elongation and force of elongation. The hard segments are responsible for the restoration of the molecule chains after the deformation. They comprise short-chain crystalline regions. As fixed points, the primary task of the hard segments is preventing the polymer chain from sliding off under the effect of mechanical forces. After a deformative extension the restoring forces present in the elastomer cause a contraction almost to the starting length. The remaining difference in length is referred to as residual elongation.
In general, the polyurethane elastomers are obtained according to a two-stage process in which in a first reaction step higher molecular diols are converted with diisocyanates to prepolymers, which, in a second step, react with so-called chain lengthening means to form high-molecular products. In the first reaction step excess quantities of diisocyanate are used so that the prepolymer is terminated at both ends by an isocyanate group. The chain lengthening means are bifunctional, low-molecular compounds with terminal reactive hydrogen atoms, most often dihydroxy or diamine compounds. They react with the prepolymers to form the corresponding carbamic acid derivatives, i.e. the polyurethane elastomers, respectively polyurea urethane elastomers. In the macromolecule chains the soft segments formed of the higher-molecular diols alternate with the rigid hard segments formed by the reaction of the chain extenders with terminal isocyanate groups.
The different chemical compositions of hard and soft segments as well as their different polarities and molecular weights leads to demixing. Hydrogen bridge bonds between adjacent chains lead to the fact that the hard segments become juxtaposed in parallel. The long mobile molecule chains in between form entanglements and loops which during elongation of the wide-mesh network become detached and elongated. The interaction between hard segments prevents the plastic flow of the molecule chains in the elongated state. The elongation of the macromolecules is tied to a transition into a higher-ordered conformation and a decrease of entropy. Due to the thermal motion of the molecules, they return to the state associated with higher entropy of the looping after relief of loading. Under strong mechanical loading, however, a permanent elongation can occur so that the polymer chains slide off in the elongated state.
The hard segments in polyurethane elastomers have an elongation-limiting cross linking function as well as also a decisive influence on the thermal behavior, respectively the melting range. The urea groups formed when using diarnine chain extenders are more polar than the urethane groupings formed through glycol extension. The stronger hydrogen bridges in the polyurethane elastomers lead to greater demixing occurrences of hard and soft segments, and thus better elastic properties as well as also higher hard segment softening points.
From the literature various spinning methods for the production of elastomer yarns are known. The major portion of the elastomer fibers is produced according to the dry-spin method. Here a highly viscous solution is pressed through multihole nozzles in perpendicularly disposed heated spinning shafts. Simultaneously, hot air is supplied in order to evaporate the solvent and to solidify the filaments. The spinning rate is in the range from approximately 200 to 600 m/min. Due to the low dwelling time in the spinning shaft, and in order to ensure complete solvent removal, the single titers are limited to a maximum of 20 dtex. The production of the end titers takes place by joining corresponding single capillaries with the application of a false torque.
In wet-spinning the prepared polymer solutions are spun into a coagulation bath. The yarns are subsequently washed, bonded one to other and dried. The draw-off rate is approximately 100 m/min.
The reactive spinning method combines a chemical reaction with the spinning process. The prepolymer is extruded through multiple hole nozzles into a spinning bath of, for example, aliphatic diamines. On the surface of the filament an immediate isocyanate-amine reaction to polyurea urethanes take place. The relatively solid skin permits the secure spinning process. The interior of the fiber is cured through treatment with hot water or through the reaction with diamine alcohol or toluene. The spinning rates are in the samerange as in the wet-spinning process.
In melt-spinning the polymer is melted in a cylinder and the melt is pressed through the die plate with gear pumps or extruder worms, the exiting fibers solidify in the air. The advantage of this technology lies in the solvent-free spinning into yarn. This economically significant method has until now not been applied to polyurethane elastomers lengthened with amino-containing chain extenders. These polymers usually decompose before melting due to the high softening point of the hard segments.
Commercially available melt-spun elastomeric polyurethane fibers therefore are based on hydroxyl group-containing chain extenders. F. Foume (Chemiefasern/Textilind. 96 (1994), 392-398) reports about the Japanese manufacturer Kanebo who operates pilot plants in which the polyurethane-ester fiber “Lobell” is obtained according to the melt-spin method. The melt-spun polyether-ester yarns “Rexe” and “Spantel” of the companies Teijin, respectively Kuraray Co., have been available on the market since 1993. The mechanical properties of these fibers are not satisfactory because here in the hard segments urethane groups are present instead of urea groups which, as explained above, lead to lower mechanical stability due to weaker hydrogen bridge bonds.
An improvement of the mechanical textile properties was attained through covalent cross linking of the hard segments (F. Hermanutz, P. Hirt, Chemiefasern/Textilind. 96 (1994), 388-391). By using double bond-containing chain extenders, centers were created for this purpose which are capable of being cross linked. Through electron or UV radiation subsequent polymerization can be triggered after the spinning. These polyurethane elastomers, however, are subject to the restriction that the diamine chain-extending polyurethane elastomers are not melt-spinnable. These known polyurethane elastomers, furthermore, exhibit strong yellowing after exposure to electron or UV radiation.
SUMMARY OF THE INVENTION
It is therefore the object of the present invention to make available polyurethane elastomers which, due to suitable melting points, can advantageously be melt-spun and, optionally following suitable secondary treatment, for example, by radiation with high-energy radiation, lead to fibers with improved mechanical properties.
According to the invention this object is solved through a polyurethane elastomer which comprises structural units of the following type:
wherein:
the grouping—O—R
1
—O represents a macrodiol group of a molecular weight from approximately 500 to 10000,
R
2
a bivalent aliphatic, cycloaliphatic, and/or aliphatic-cycloaliphatic group; and X a short-chain, olefinically unsaturated group,
Y NH or O as
n an integer from 1 to 10, and
m an integer of at least 4.
In a polyurethane elastomer accordingly the moieties R
1
, R
2
and X are of significance.
The moiety R
1
can be traced back to a macrodiol. Preferably linear diols are substantially used which, in addition to the terminal hydroxyl groups, carry no further groups reacting with isocyanates. The macrodiols have a molecular weight of a
Hermanutz Frank
Hirt Peter
Oess Oliver
Oppermann Wilhelm
Schweizer Michael
Bucknam and Archer
Rhodia S.A.
Sergent Rabon
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