Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – From carboxylic acid or derivative thereof
Reexamination Certificate
2001-06-20
2003-05-20
Hampton-Hightower, P. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
From carboxylic acid or derivative thereof
C528S312000, C528S322000, C528S323000, C528S329100, C528S332000, C528S335000, C528S336000, C526S064000, C526S066000, C524S600000, C524S606000, C264S512000, C264S513000, C264S514000, C264S515000
Reexamination Certificate
active
06566486
ABSTRACT:
The application provides an at least two-stage process for the production of polyamides and the use of the polyamides obtained therefrom for applications such as, for example, injection moulding, extrusion, extrusion blow moulding and thermoforming.
Polyamides are a class of polymers which have proven successful for many years. They are characterised in particular by easy processability, very good mechanical properties, very good electrical properties, elevated heat resistance, good resistance to chemicals and very good surface quality.
Polyamides may be produced using various processes and be synthesised from very many different units and, alone or in combination with processing auxiliaries, stabilisers, polymeric alloying components (for example elastomers) or also reinforcing materials (such as for example mineral fillers or glass fibres), may be provided with specific combinations of properties to yield materials for specific applications.
The properties of polyamides may be improved by addition of elastomers, for example with regard to the impact toughness of, for example, reinforced polyamides. The large number of possible combinations makes it possible to create a very large number of products having the most varied properties.
Numerous processing methods are known for the production of polyamides, wherein, depending upon the desired finished product, different monomer units, various chain-transfer agents to establish the desired molecular weight or also monomers having reactive groups for subsequently planned post-treatments (for example amino groups or sulfonate groups to improve the dye affinity of fibres for acidic or basic dyes respectively).
Industrially significant processes for the production of polyamides proceed, without exception, by melt polycondensation. In this context, hydrolytic polymerisation of lactams is also understood as polycondensation.
However, due to the very rapid increase in melt viscosity which accompanies a rise in molecular weight, these processes only yield relatively low molecular weight products, as an excessively high melt viscosity gives rise to various problems.
Temperature control and removal of the water of reaction accordingly become increasingly difficult, while the long reaction time at the elevated temperatures which are required results in more extensive secondary reactions and gel particle formation, which may dramatically impair the quality of the final product. Spinning also becomes increasingly difficult at very high melt viscosities.
Solid phase post-condensation (SPPC) here provides decisive advantages. Due to the far lower reaction temperatures (approx. 150 to 230° C. in comparison with 250 to 280° C. in the case of melt condensation), the risk of unwanted secondary reactions and gelation is reduced. Since the material to be subjected to post-condensation comprises defined particles having an interstitial volume, it is not problematic to maintain a uniform reaction temperature and to remove the residual water. The particle form also means that there are no spinning problems.
However, the achievable molecular weight is limited with SPPC too, as the viscosity values of the products level out to a plateau. While the height of this viscosity plateau may indeed be raised by increasing the temperature, such an increase then in turn gives rise to problems such as secondary reactions and gelation.
There is accordingly a requirement for a process which, in an industrially readily controllable manner, permits the production of high viscosity polyamides in a short reaction time and under mild conditions.
It would furthermore be desirable to be able reliably and rapidly to produce polyamides which exhibit very high melt viscosities at low shear rates, as are required, for example, for extruding large tubes or for extrusion blow moulding of large hollow mouldings (for example automotive ventilation tubes or tanks or automotive intake manifolds).
Known processes for the production of high viscosity polyamides are solid phase post-condensation of medium viscosity linear polyamides and the incorporation of branching agents into the polymer chains. The latter may be performed during polycondensation in a batch process or in a continuous tubular reactor. The incorporation of branching agents such as tri- and tetrafunctional carboxylic acids or amines, which are introduced with monomers in the polycondensation reaction, normally gives rise to non-homogeneous products with a strong tendency towards forming gel particles and specks. According to EP 0 345 648 B1, it is possible to reduce the formation of specks by maintaining certain quantity ratios between the feed materials.
As an alternative to incorporating branching agents during polycondensation, branching agents may also be incorporated into polyamides by compounding (for example in twin-screw extruders). EP-A-774 480 describes a process in which trimesic acid is incorporated into a polyamide prepolymer by compounding and then subjected to solid phase post-condensation. Stated advantages of this process are a, readily controllable molecular weight, good flowability and overall crystallinity while avoiding formation of gel particles and crosslinking. A disadvantage of this process is the additional processing step of compounding in comparison with incorporation of the branching agent during the polycondensation reaction.
Incorporating branching agents during polycondensation usually gives rise to partially crosslinked structures or gel particles and to very high viscosities, which in particular give rise to problems during spinning of the polymer melt. Similar problems are also observed when incorporating branching agents during compounding.
It has surprisingly been found that incorporating certain branching agents, such as for example polyfunctional amines, which contain at least one secondary amino group or are reacted with salts containing such amines and dicarboxylic acids, in a two-stage process does not exhibit the disadvantages of the prior art.
In particular with trifunctional amines (such as for example diethylenetriamine), preferably in quantities of 0.1 to 1.0 wt. %, particularly preferably in quantities of 0.2 to 0.8 wt. %, an initially free-flowing, largely unbranched and gel particle-free polyamide which may very readily be spun and pelletised is obtained during polycondensation in
Incorporating branching agents during polycondensation usually gives rise to partially crosslinked structures or gel particles and to very high viscosities, which in particular give rise to problems during spinning of the polymer melt. Similar problems are also observed when incorporating branching agents during compounding.
It has surprisingly been found that incorporating certain branching agents, such as for example polyfunctional amines, which contain at least one secondary amino group, in a two-stage process does not exhibit the disadvantages of the prior art.
In particular with trifunctional amines (such as for example diethylenetriamine), preferably in quantities of 0.1 to 1.0 wt. %, particularly preferably in quantities of 0.2 to 0.8 wt. %, an initially free-flowing, largely unbranched and gel particle-free polyamide which may very readily be spun and pelletised is obtained during polycondensation in a continuous polycondensation process. Polycondensation is preferably performed in the presence of conventional catalysts and chain terminators/chain-transfer agents. The polyfunctional amines are used in combination with dicarboxylic acids or more highly functional carboxylic acids. The molar ratio of tri- or more highly functional amine to dicarboxylic acid is thus preferably >1. A pseudoplastic PA, which exhibits low viscosities at elevated shear rates and very high viscosities at low shear rates, is obtained in a second step by solid phase post-condensation.
The application accordingly provides a process for the production of polyamides, which is characterised in that, in a first reaction step, suitable monomers such as caprolactam or an aliphatic aminocarboxylic acid are reacted wit
Bruder Friedrich-Karl
Dietrich Hans-Jürgen
Gittinger Andreas
Joachimi Detlev
Morhenn Heinrich
Bayer Aktiengesellschaft
Gil Joseph C.
Hampton-Hightower P.
Preis Aron
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