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
2000-04-10
2001-07-17
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...
C528S308000, C528S308600, C528S50200C, C528S503000, C428S480000, C524S777000, C524S779000, C524S765000
Reexamination Certificate
active
06262185
ABSTRACT:
The present invention relates to the use of thermoplastic polyester molding materials containing
A) from 80 to 100% by weight of a polyalkylene arylate having a half-width of the crystallization isotherms of ≦5° C.
B) from 0 to 20% by weight of further additives,
the percentages by weight of components A) and B) summing to 100%,
for the production of moldings by blow molding, profile extrusion and/or tube extrusion.
The present invention furthermore relates to processes for the preparation of the molding materials which can be used according to the invention and the moldings obtainable hereby.
Polyesters are distinguished by low water absorption and good dimensional stability as well as solvent resistance.
Mixtures of polyesters with other additives have long been known. However, the known polyesters can be processed to blown moldings only to a limited extent. Blow molding generally involves extruding a tube of polymer melt, which hangs between the two half-shells of the opened mold. The mold is then closed and the polymer tube is pressed against the mold by internal gas pressure, cooled and removed from the mold.
An important precondition for this processing is that, during extrusion, the polymer tube does not break in the periods when it hangs freely between the molds, so that the shaping process can be completed. It is also desirable that the tube does not sag, since this results in small wall thicknesses in the upper half and larger wall thicknesses in the lower half. Hollow bodies having different wall thicknesses are not suitable for use since the load capacity is generally limited by the point having the smallest wall thickness. The molding materials known from the prior art can therefore be used for the blow molding method only to a very limited extent since the tube strength is too low.
Usually, high molecular weight polyester which are prepared by a batchwise method, for example by polycondensation and subsequent solid-phase postcondensation, as described, for example, in DD-A 138074, DE-A 30 12 692 and DE-A 30 22 076, were used for blow molding.
The disadvantage of these methods are long residence times and an undesirable yellow color of the resulting polyester due to thermal load.
The compounding of high molecular weight polyesters with other additives which, depending on the type and amount, influence the desired properties and the processing of the polyester, is however not possible since a decrease in molecular weight occurs during compounding, so that—even when high molecular weight starting polymers are used—materials unsuitable for blow molding are always formed.
The use of polyesters, in particular polybutylene terephthalate (PBT) for the production of optical waveguide sheaths is disclosed, for example, in DE-A 258 859, DE-A 43 03 116, DE-A 42 12 146, DE-A 42 19 607, DE-A 41 42 047 and EP-A 336 806.
According to JP-A 08/227 030, a PBT suitable for covering optical waveguides has an intrinsic viscosity of 1.2, a terminal carboxyl group content of 40 meq/kg of PBT and nucleating agents, phosphorus compounds and sterically hindered phenols as stabilizers. The difference between melting point and initial crystallization temperature should be >30.
JP-A 08/146 261 describes the addition of polycarbonate and stabilizers to polyesters for improving the performance characteristics.
The polyesters known from the prior art are suitable only to a limited extent for extrusion applications, in particular for optical waveguide (OWG) sheaths.
This is specific, on the one hand to the material, for example PBT has only a moderate tendency to crystallize. On the other hand, the special process conditions in the OWG production give rise to difficulties. The production is carried out by the extrusion method by means of a crosshead (similarly to cable sheathing), in which a cold water bath and also cold gel (interior filling of the tubes) are often used; furthermore, the high take-off speeds have an additional quenching or supercooling effect. The hot melt tube at about 260-270° C. is exposed to a cold gel or water immediately after its emergence from the crosshead (mm or a few cm).
If the polyester does not have a sufficiently high tendency to crystallization, supercooling of the melt occurs in this critical range. Consequently, sufficient crystallization of the melt (and hence the solidification thereof) is suppressed to such an extent that the extrudate is deformed to an oval cross-section by the downstream apparatuses (take-off, etc).
Other consequences of a low tendency to crystallization are, for example, poor mechanical properties, low dimensional stability and insufficient stability to hydrolysis (the latter is however also determined by the level of terminal carboxyl groups).
The following extrudate parameters have a substantial effect on the operability of the optical waveguides:
Extrudate Surface:
Rough uneven surfaces (on the inside) lead to an increase in the damping of the glass fibers and hence to an adverse effect on the transmission quality. A difference in length of the main cross-sectional axes from 0.05 mm, corresponding to <2% of the external diameter, is required.
Concentricity:
Impermissible deviations in the concentricity lead to twisted structures, which are no longer symmetrical and thus limit the capacity of a cable group.
Stability to Hydrolysis:
The tube material must be sufficiently resistant to water or the humid atmosphere so that problem-free installation is possible without the danger of breaking, even after a relatively long time. The after-shrinkage should be <1%.
After-Shrinkage:
If the after-shrinkage is too great, the tube cross-section is reduced so that the glass fibers have less space, the damping increases and the transmission quality suffers.
It is an object of the present invention to provide high molecular weight, readily crystallizing polyester molding materials which can be readily processed continuously and independently of the type of starting materials to give blow moldings, extruded profiles or extruded tubes.
The moldings should have good surfaces and good dimensional stability (accuracy of calibration), stability to hydrolysis and low after-shrinkage.
We have found that this object is achieved, according to the invention, by the use of polyester molding materials as claimed in claim
1
. Preferred embodiments and processes for the preparation are described in the subclaims.
The molding materials which may be used according to the invention contain, as component A), from 80 to 100, preferably from 90 to 100, particularly preferably from 50 to 85, % by weight of a thermoplastic polyalkylene arylate.
In general, polyesters based on aromatic dicarboxylic acids and an aliphatic dihydroxy compound are used.
A first group of preferred polyesters comprises polyalkylene terephthalates having 2 to 10 carbon atoms in the alcohol moiety.
Such polyalkylene terephthalates are known per se and are described in the literature. They contain an aromatic ring in the main chain, which ring originates from the aromatic dicarboxylic acid. The aromatic ring may also be substituted, for example by halogen, such as chlorine or bromine, or C
1
-C
4
-alkyl, such as methyl, ethyl, isopropyl, n-propyl and n-butyl, isobutyl and tert-butyl.
These polyalkylene terephthalates can be prepared by reacting aromatic dicarboxylic acids, esters thereof or other ester-forming derivatives with aliphatic dihydroxy compounds in a manner known per se.
Examples of preferred dicarboxylic acids are 2,6-naphthalenedicarboxylic acid and terephthalic acid and mixtures thereof. Up to 30, preferably not more than 10, mol % of the aromatic dicarboxylic acids can be replaced by aliphatic or cycloaliphatic dicarboxylic acids, such as adipic acid, azelaic acid, sebacic acid, dodecanedioic acids and cyclohexanedicarboxylic acids.
Among the aliphatic dihydroxy compounds, diols of 2 to 6 carbon atoms, in particular 1,2-ethanediol, 1,3-propanediol, 1,4-butanediol, 1,6-hexanediol, 1,4-hexanediol, 1,4-cyclohexanediol, 1,4-cyclohexanedimethanol and neopentyl glycol and mixtu
Braune Peter
Fisch Herbert
Heitz Thomas
Pellkofer Erich
Schneider Georg
Acquah Samuel A.
BASF - Aktiengesellschaft
Keil & Weinkauf
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