DD161134A1 - METHOD FOR THE PRODUCTION OF HIGH-MOLECULAR POLYAMIDE - Google Patents

Abstract

The invention describes a process for the preparation of polyamide-6 of higher viscosity from a polyamide-6 low viscosity by post-polycondensation below the melting point. The low viscosity polyamide is prepared by adding small amounts of an alternating copolymer of maleic anhydride and an alpha-olefin.

Description

-2- 222

The polymers have a molecular weight between 5,000 and 500,000. The addition of the copolymer to the polyamide is expediently carried out directly in the polymerization batch. But it is also possible, the copolymer before the discharge of the polyamide from the polymerization plant, e.g. by an additional extruder, in the form of a masterbatch. The copolymer is not extracted in the subsequent extraction with water. The extract water can be partially or totally recycled after its concentration in a known manner in the polymerization. The Nachpolykondensation is not affected by the proportion of the return of the extract. In special cases, especially when particularly high molecular weights are to be achieved, it may be expedient to incorporate the copolymer into the polyamide via an extruder. The polyamide can be used in extracted or unextracted form. The post-polycondensation is carried out in a known manner at temperatures of about 443 to 473K with a duration of 5-24 hours under nitrogen or in vacuo.

Embodiment 1

Per hour, 100 parts by weight of epsilon-caprolactam, 0.5 part of water and 0.01 part of an alternating copolymer of alpha-methyl-styrene and maleic anhydride as molten mixture at a temperature of 383 K are introduced into a VK-tube. The mixture is polymerized at temperatures of 513 to 538K and spun into a water bath after a lapse of 18 hours. The strands are granulated after solidification, extracted and then dried. The extract water is concentrated to 98-99% lactam / oligomer mixture and returned to the process. The whole process runs continuously. The extracted and dried granules are then annealed at 453 K 8 hours under DD-PS 91566 under nitrogen. The granules have a _ridge of 4.08. If the extract is not recycled, a viscosity of 4.15 is achieved. If work is carried out under the same conditions with an addition of 0.0025 part of phosphoric acid, then without the return of the extract only one η _Γβ! reached from 3.64.

Embodiment 2

In a 1 l glass flask, 470 g of epsilon-caprolactam, 30 g of epsilon-aminocaproic acid and various amounts of alternating olefin / maleic anhydride copolymers are heated to 523 K under nitrogen for 5 hours. Thereafter, the products are poured into water, crushed, extracted and dried. Subsequently, samples of the polymers are heated to 453K under nitrogen for 8 hours.

Olefin of additive η _ΓβΙ extracted η _{Γβ (} according to the copolymer % annealing alpha-methyl styrene 0.5 2.84 4.10 propylene 0.05 3.42 4.43 vinyl acetate 0.01 3.37 4.22 Isobutylvinyiäther 0.05 2.96 4.13 propylene 0.5 3.99 5.90

Embodiment 3

In an extruder with a screw diameter D of 60 mm and a screw length of 20 D, 30 kg of polyamide-6 per hour become η _Γβ | = 2.74, which have been powdered with 0.4% of an alternating copolymer of propylene and maleic anhydride homogenized. The temperatures are 493-523 K. The emerging melt is cooled in water and granulated. The granules have a η _Γβ , = 3.98. Subsequently, the granules are annealed at 453K for 8 hours under nitrogen, thereby an η _Γβ , reached of 5.82.

Claims (2)

1. A process for the preparation of high molecular weight polyamide-6 by Nachpolykondensation of polyamide-6, which was obtained by known methods and in known devices, optionally with partial or total recycling of the concentrated aqueous extract, at temperatures just below the melting point in a vacuum or inert gas atmosphere , characterized in that a polyamide-6 is used, the 0.005 to 0.5%, preferably 0.01 to 0.1% of an alternating copolymer of maleic acid or itaconic anhydride an alpha-olefin of general formula ^CH 2 ⁼ C ^ R ^ in which R ₁ and R _{2 is} a hydrocarbon radical having one to 10 carbon atoms and / or hydrogen or R _{1 is} hydrogen and R _{2 is} an ester or ether group contains. -1- 222 Invention claims: 2. The method according to item 1, characterized in that are used as copolymers of maleic anhydride and ethylene, propylene, 2-methylpropene-1, 2,4,4-trimethylpentene-1 or alpha-methylstyrene. Process for the preparation of high molecular weight polyamide
Field of application of the invention The products according to the invention are used in the plastics processing industry for the production of films, injection molded parts and semi-finished products. Characteristic of the known technical solutions For the production of films, semi-finished products and hollow bodies as well as particularly impact-stressed parts made of polyamide-6, products with high molecular weights are required. Measured by the relative solution viscosity (according to TGL 20055) this means that values above 3.6, suitably above 4.0 must be achieved. The preparation of such polyamides is carried out (for example according to DE-AS 1115017, DE-PS 1079834, DE-AS 1179370 or DD-PS 91566) by postpolymerization of the polyamides shortly below the melting point in vacuo or inert gas atmosphere. The starting material is a polyamide-6, which is prepared according to the known methods of hydrolytic polymerization, optionally with the addition of specific catalysts such as phosphoric acid or its salts in so-called VK tubes at residence times of 12 to 36 hours. The residence times in the post-polycondensation are again about 5 to 24 hours. As already mentioned, it is usually customary to prepare the polyamides intended for postpolycondensation with addition of acids or salts of the phosphorus. If one uses polyamides prepared without this additive, e.g. according to other technically customary methods with the addition of acetic acid or only water, the postcondensation is very slow. In addition, temperatures are required that are already close to the softening point, which makes the technical implementation of the method extremely difficult. When using derivatives of phosphorus in the form of its acids and salts, lower temperatures and shorter times can be used. Here, however, there is another difficulty. It has become customary to reduce the concentrated extract obtained in the production of polyamide-6, consisting of epsilon-caprolactam and its low molecular weight oligomers, to the process without further workup. Since the phosphoric acids or their salts are extracted to a high percentage and accordingly find themselves in the concentrated extract, a certain level of these products sets in with continuous recycling of the extract in the polyamide. The height of this mirror determines the conditions (temperature, residence time) in the post-polycondensation. However, it is not always possible to ensure the continuous recycling of the extract. In this case, the phosphorus level changes in the polyamide, which leads to more or less large viscosity fluctuations in the post-polycondensation. For the preparation of high molecular weight polyamides, additions of crosslinkers before, during or after the polymerization are also recommended. When the crosslinker is added before or during the polymerization, it is generally conducted only to solution viscosities of n, _ret = 2.5-3.5. This is usually followed by a thermal after-treatment in the solid state in order to obtain higher viscosities, since the technical handling of large quantities of highly viscous melt is complicated and difficult. Crosslinkers recommended for this process are predominantly brslactams added in amounts of 1 to 3% and more. The introduction of the crosslinker after the polymerization is carried out in the extruder or mixer. For this purpose recommended connections are z. As carbonic acid or dicarboxylic acid esters of phenols, epoxy compounds or diisocyanates. These products are not physiologically harmless or discolor the polymers. The crosslinking in the extruder is relatively fast, but sometimes a repeated extrusion process is required. Object of the invention The aim of the invention is the production of high molecular weight polyamide by post-polycondensation of polyamide-6 shortly below the melting point. Explanation of the essence of the invention It was therefore an object to make the known production of high molecular weight polyamide-6 by post-polycondensation shortly below the melting point from the side of the feedstock so that changes in the return of the extract in the preparation of the feedstock have virtually no influence on the course of Nachpolykondensation. The object is achieved by a process for the preparation of high molecular weight polyamide-6 by Nachpolykondensation of polyamide-6, which was obtained by known methods and in known devices, optionally with partial or total recycling of the concentrated aqueous extract, at temperatures just below the melting point in a vacuum or inert gas atmosphere by using a polyamide-6 containing 0.005-0.5%, preferably 0.01-0.1%, of an alternating copolymer of maleic or itaconic anhydride and an alpha-olefin of the general formula CH ₂ = c ' _R \ in which R1 and R2 is a hydrocarbon radical having one to 10 carbon atoms and / or hydrogen or R1 is hydrogen and R 2 is an ester or ether group. Alternating copolymers of this type are z. B. copolymers of maleic anhydride or itaconic anhydride and ethylene. Propylene, 2-methylpropene or a technical mixture of 2-methyl propene and butene-1, 3-methylpentene-i, _2,4-f 4 trimethylpentene-1, vinyl acetate or vinyl methyl ether, styrene or alpha-methylstyrene. These copolymers can be prepared by free-radical polymerization by known processes, for example according to DD-PS 128164.